The big problem you have here is MAD (Multiple Attribute Dependency). The bane of multiclass characters, MAD makes it difficult to pull off certain class combinations. As a Wizard, you're going to want as much Int as possible. As a Monk, you want to get both your Dex and your Wis up as high as you can. And since you've said you want to be a tank, you might even want to get a better Con score at some point.
You get 5 ability score increases over the course of your career - enough to max out your Int, then probably your Dex, leaving your Wis and Con scores exactly as they are now. (And that's assuming there's no feats you want.)
You can improve on this situation slightly: assuming I've done my maths correctly, it looks like you've used point-buy to come up with your ability score array. If you dump the Str and Cha scores back to 8, it gets you an extra 4 points which you can use to bring your Dex or Wis up to 16 (or your Con up to 14, but I wouldn't recommend that).
The way around the MAD problem is to pick classes which align slightly better, attribute-wise. For example, for a spellcaster Monk, picking a spellcasting class based on Wis (i.e. Druid or Cleric) would reduce your problems a long way. Unfortunately, there are no arcane spellcasting classes based on Wis.
Your next problem is that you've picked 5 skills that you want to be good at. The combination of class and background only gives you 4, and getting more requires a heavier investment than you can really afford, so you're not going to be able to get proficiency in all 5. The obvious one to ditch is Perception, because neither the Wizard class, the Monk class, or the Sage background give proficiency in it. That said, it's probably the most important skill in the game, so maybe you want to customize your background and drop something else. I'd suggest that one of the Int-based skills would be the best not to have proficiency in, since you'll have a good Int anyway so you'll still be ok at it.
Ignoring all that, let's assume that you're going ahead with a Wizard/Monk and address your specific questions.
Should I even multiclass, will it give anything at all? If yes, in what proportion? Will the Way of the Four Elements chosen or will other tradition give more benefits?
The 1st level of Monk gets you Unarmoured Defense and Martial Arts, which is enough to make it a good investment. Further levels in Monk take a lot of investment to get anything particularly worth having, so I'd recommend sticking with Monk 1/Wizard 19. If you do decide to take more Monk levels, make sure you do it in multiples of 4 so that you don't lose an ability score improvement. If you do take enough levels to get a Monk tradition, Way of the Four Elements is probably not a good choice. Your Wizard spellcasting will far outstrip the little bits of spellcasting it offers. The Way of Shadows likewise just gives some spells you have access to anyway. The Way of the Open Hand is probably your best bet.
Should I get a familiar?
What you have to understand is that familiars don't really boost your combat ability in any way. They offer great utility, as scouts/messengers, particularly if you pick something like the Hawk or Owl that's good at Perception. Regardless, it's not a big investment, just 5 gp and a single 1st-level spell (of which you have a minimum of 8 at Wiz 2), so I'd honestly recommend getting a familiar to anyone playing a Wizard.
What school to specialize in?
Abjuration is probably your best bet for helping you survive in melee. Necromancy is also good at this as long as you're killing things with spells. I went into a lot more detail about this in my answer here, so I'd suggest taking a look at that rather than me reproducing it here.
What spell choices can support the theme most?
There are now no Wizard spells that will directly boost your unarmed strikes, so your best bet for using a spell to increase your fighting abilities is probably just casting Haste on yourself. Other than that, your best bet for melee spellcasting is probably Vampiric Touch, particularly if you choose to specialize in Necromancy. Again, I went into a lot of detail about this here, so I'll keep self-linking instead of writing it all out again.
Feats or ability increases?
Ability score increases, definitely. You really need them, and there aren't any feats that you need as badly. War Caster is the usual choice for melee spellcasters, but you're not planning on holding any weapons or shields, so you don't really benefit from it much. Not to sound repetitive (it's actually a different answer this time), but I went into a lot of detail about which feats are good for a melee spellcaster in my answer here. But for you, I'd definitely suggest sticking to ability score increases.
Any magic items that can help?
Quite a few, actually. The ones you would want the most are the ones that would help you with your MAD problem: The Amulet of Health, the Headband of Intellect, Ioun Stones of Agility, Fortitude, Insight, or Intellect, Manuals of Bodily Health or Quickness of Action, and Tomes of Clear Thought or Understanding.
The other item that would be particularly useful for you specifically is the Bracers of Defense. Obviously, there are a lot of other items that are useful for everyone in general, or spellcasters in general. If you're playing Hoard of the Dragon Queen, there's an item called the Insignia of Claws that you definitely want to get if you can.
Best Answer
Don't use CR
I don't think CR is going to solve your problems.
It would be great if you could plug in all the info into a calculator and pull out a number which will tell you how challenging the fight will be. And to be fair, there are a lot of very good CR calculators around.
However, the problem I have with them is that CR isn't very good from the start. CR is a rough approximation, but even if you calculated the CR perfectly, you still need to examine the situation more closely.
Asymmetrical Balance
One of the big problems you are going to have, is that NPCs are not PCs. PCs have incredible damage, but not much HP. Your wizard is the same, they have very little survivability, but a lot of damage. That's not the way NPCs should be built.
Take a quick look at your wizard; 30hp + False Life (lvl 3 slot: 2.5 + 4 + 10 = 16.5) = 47ish hp, 14AC. That's not a lot. Many level 3 classes will be dealing 1/3 to 1/2 that much damage on average. 14AC isn't a challenge for level 3 martial classes to hit either. A character could 1 hit that wizard with a luck roll and a crit.
And you have 3 lvl 3 PCs beating on this wizard, every turn. It's likely the wizard will be down before their initiative comes up, heck it's likely that one player won't even get a turn.
Difficult single enemies are easy to beat
Any time a monster is solo, it's vastly easier to beat. Lower level PCs can beat it down with their action economy. There's not much way around this, that's why stronger monsters have legendary actions.
So, what to do instead?
Firstly, don't use PC levels for an NPC. Pick the spells and features you want, and attach it to an existing monster of the right CR.
Secondly, make sure there are always minions in the fight. 1v3 isn't fair. 5v3 isn't fair either, but it's a lot more fun if the players win when the odds are against them! Even if they are only CR 1/4 skeletons, being outnumbered helps with the action economy, and it's fun.
Thirdly, play test. Yes I know, it's a pain, it would be great if you can just plug it all into a formula, right? But play testing will give you a much better understanding. There is no way to accurately predict how your players will react, but using their PCs to test is the closest you can get. It's not as hard as you may think. If you have their character sheets it's pretty straight forward.
Or, like I do, throw all that away
I used to play test, to make sure everything went smoothly. But now I don't. It doesn't matter if things do not go smoothly, actually I personally prefer it. I'm not saying you should throw vastly stronger things at the players, but a little too strong is fine.
If players run in and steamroll your wizard? So what. There are other enemies in the game, don't sweat it.
If players struggle with the wizard, losing a lot of hp and resources? Again, so what. It's up to them to manage their resources, and handle fights and pacing.
I find this works a lot better. The story emerges from the players actions instead of from my head. This makes them happier since their actions are the story, and me happier because I don't have to worry making a good story for the players. This is part of an overall player-driven philosophy to running games. I'm not going to try turn you away from narrative games in one swoop, but if you think about facilitating your players actions instead of dictating them, then you may find unbalanced encounters to be less of a problem.