While T2 is definitely a direct sequel of T1, you have to realize, these are both games that focus on "kill everything that moves" and "loot everything you see". The storyline is only there to help players become familiar with areas and the enemies that arise from them, but isn't necessary play T1 over T2.
Honestly though, T2 is a completely reworked version of T1 that features a whole slew of new improvements, as well as dedicated modding support, etc.
Consider this, it's very much like the L4D series. While L4D had a storyline, and so did L4D2, the story lines were only vaguely connected, but the game was more about a zombie co-op game. This isn't to say the storyline was non-existent, but it's there to guide players to understand what's happening around them. Gameplay-wise, much like TL2, L4D2 is a very very nice upgrade to L4D, in that there are more weapons, more game modes, more special infected, and other nice sweets.
Basically, consider T2 over T1 as a nice upgrade, with more features than its predecessor. If you really really care about storyline, by all means, it doesn't hurt to play T1. If you really like gameplay, then I'd say it really doesn't matter.
Strength adds to Weapon Damage for EVERY class. However, if you are an Embermage, you are likely using Wands or a Staff. If you are using Wands or a Staff, then you gain Weapon Damage from increasing your Focus. The reason for this is that Focus increases Magic Damage, and if you look at a staff or a wand, you will notice that they don't do any physical damage - it's all elemental!
Now, there might be a couple reasons to increase your Strength as an Embermage - it WILL increase your Weapon Damage and Critical Damage, and may be useful to be able to equip certain gear. However, I find that the benefits of increasing Strength are minimal compared to the benefits of increasing Focus. Focus gives you a greater mana pool, allows you to equip higher-level Embermage-specific gear sooner, and ALSO increases your Weapon Damage by the same amount as increasing Strength! Therefore, I recommend increasing Focus as your most important attribute, with Vitality following, then Dex sprinkled in. (Usually for gear requirements.) I sometimes increase Strength if certain gear requires it and I don't want to wait until a higher level, but almost never otherwise.
Also, just a caution - Weapon Damage and Weapon DPS are NOT the same. Weapon DPS is a simplified display of a weapon's damage output, derived from a formula using Attack Speed, Weapon Damage, and more. Weapon Damage is the damage per hit of the weapon, as seen in your character stats screen.
The reason I mention this is because some class skills (I think Outlander skills, mostly) use Weapon Damage as a modified ("50% of Weapon Damage") and some use Weapon DPS ("50% of Weapon DPS"). So be sure to pick the weapons and skills that compliment each other best!
Another caution - some spells use Weapon DPS to calculate damage. Some do not, and are based on your character level and the level of the spell. (Hailstorm, for example.)
It sounds like the setup you've chosen will work just fine with a high-Focus character build, and feel free to choose the staff with the highest weapon DPS if you're looking to deal the most damage. And don't forget to have fun! :)
Best Answer
The most important factor that comes from vitality is the +armor bonus%.
This becomes very prominent for melee fighters late game as monsters will start hitting you for really hurtful damage. So you would want to stack up all the armor you can. Note this % increase also affects elemental armor which is even more critical.
Let me give some numbers, in Act III you will be encountering monsters who hit for about 800 damage, while the armor you can afford to wear will be around 400. Even at that level 400 dmg will take out a good chunk off your health even at 40-50 levels. (These are approximate numbers, it may vary game to game) Imagine you have a nice 50% bonus on all armors cause of vitality. that makes your armor 600. which means you just reduced damage from 400 to 200. You will be able to hold your ground longer and take more hits.
Some of the champion mobs deal even bigger damages than those numbers, and may outright kill you when you least expect it.
Vitality also gives you block Chance if you are using a shield. As of update 1.13 the block chance cap has been upped from 50% to 75%. 500 points in VIT gives the character around 50% Block Chance. This might not be feasible but shield based builds will rely on VIT to provide those extra block chance to nullify damage they incur.
Hope that explains Vitality for you.