[RPG] How to increase Survivability while using Warding Bonds

Question 1: None?

I don't think anyone has even bothered to make a Vampire handbook on the WOTC forums in all these years which is a black mark itself. The only scrap of optimization opinion on the Vampire comes up in the hybrid section of the optimization forums:

Vampire Summary: Lots of nice features, if only there wasn't that only having 2 surges issue and likely not wanting Vampire encounter powers. If you're going Vampire, you're doing this because your game typically has 4-6 encounters per day, not because you have 2-3.

• Stats: Dex or Cha. You get one at-will from Vampire and it will be either Dex or Cha. Not too bad other than it might limit Daily choice.

• Class Features: Solid, again, just two surges being the limiting problem and needing to get a Vampire feat to make up for it. Hurts to lose Vampire Reflexes though given only getting Cloth.

• Implement/Weapon: Ki Focus is now one of the best options. A little too poachable by MC Assassin Feats, but you get Holy Symbol as well? Two off-slot implements and a shield bonus means lots of options for picking items for your hands.

• At-Wills: At-wills are all decent.
• Hybrid Feat benefits: Near worthless. You really want Darkvision that badly, be a Drow which is one of the best races for Vampires.

Of these only Ki-Focus implements is really good and as they state, there are better avenues to approach it. As you note in your question the Vampire is a pretty terrible striker and the costs that come with creating a hybrid character are in now way balanced out by what it has to offer. The only reason to make a Hybrid vampire is, as you say, you really wanted to play a better version of the vampire class.

Question 2:

As you note, Dragonborn can cheese being bloodied with their Dragonborn Fury feature and Dragonborn Frenzy feat. Being Bloodied is not inherently bad, there are also items that key off being bloodied that could also make use of this. There's really no reason to ever MC vampire compared to other options available to players.

I was thinking about this too, so here's my build (added an additional Feat from your houserules):

Lvl 4 Tiefling, Archfey Tome Warlock

This build points to forgive the melee and AC options for a more focused caster. I liked your idea of an hybrid, but seems to me that it really needs to be an hexblade, going in the direction of the other classical builds around. Tiefling adds some interesting features, while allowing to reach 20 CHA on lvl 4, increasing the overall effectiveness and chance to hit of the few spells you can cast.

By Lvl 4 you have:

• Cantrips: Eldritch Blast, Minor Illusion, Vicious Mockery, Thorn Whip, Shocking Grasp, Thaumaturgy, Friends
• Lvl 1 Spells: Hex, Sleep, Faerie Fire
• Lvl 2 Spells: Hold Person, Phantasmal Force
• Hellish Rebuke 1\day (2d10)
• Fire Resistance
• Agonizing and Repelling Blast

I chose Archfey over Old One for several reasons:

• Spells: Dissonant Whispers and Tasha's seems kinda redundant to me, especially when you can get Hold Person at lvl 4. Sleep it's an excellent spell vs. low level mass enemies, it has no concentration and grows with spell slots. Faerie Fire can grant advantage to the entire party vs one or more hard targets. Both pacts have Phantasmal Force which is a great disable for low int enemies and fun to use too.
• Pact Powers: Fey Presence is an area disable which fits more the theme than Telepathy granted by Old One. At lvl6 Entropic ward is fine, but Misty Escape is simply awesome.

Invocations: I'd go to PimpMyBlast just because this is your only reliable source of damage in a lot of situations where CC or forced movement are not options - If all CCs fails, if you want to blast that minion in the backrows not worthy a spell, in long fights, ecc.. But if you like, you can forgo one of the blast invocations to get rituals, which can give you a bit more flexibility and a Familiar.

Feats: i'd really like going first at all costs with this build, so i'll take Alert. A well placed Sleep or Hold person the first round is no joke. Otherwise Moderately Armored can give you better ac with a shield, but going melee will require War Caster too to be a viable option.

Ability scores in order of importance: Max Cha, High Dex, High Con, Mid Wis, Low Int, Low Str

Role: cc\secondary caster

Playstyle: Disable high treat enemies as soon as you can. Use forced movement (Blast, Thorn Whip) to generate AO from allies and reposition enemies at your vantage. Minor Illusion to modify battlefield (covers, false gaps, ecc), Vicious Mockery to help ally, Shocking Grasp to disengage, Thaumaturgy\Friends as social tool.

Progression: At lvl5 you can get the infamous Devil's Sight + Darkness combo which can transform you into a walking nightmare of disabling madness, very hard to target. Lots of tactics here, disabling sight with plain movement is a powerful option, plus you attack with advantage; just take care of LOS of your allies. If you want more utility you can always get Rituals. Darkness is 1/day from Tiefling so you can also get a lvl 3 spell. While patron's spells are not that great, at lvl 3 you have 2 strong area disables (Fear and Hypnotic Pattern) and Counterspell, which is really useful if you are the only caster in the party.

Here is Lvl detailed progression:

lvl 1
Tiefling: +2 Cha, +1 Int, Thaumaturgy
Patron Fey: 1-turn Area disable 
Spells: 0 - Eldritch Blast, Minor Illusion; 1 - Hex, Sleep

lvl 2
Invocations: Agonizing + Repelling
Spells: 1 - Faerie Fire

lvl 3
Pact of the Tome: Vicious Mockery, Thorn Whip, Shocking Grasp
Spells: 2 - Phantasmal Force
Tiefling: Hellish Rebuke 1/day

lvl 4
Spells: 0 - Friends; 2 - Hold Person
Feats: Alert (from houserule 4th lvl)