My build roughly - http://skyrimcalculator.com/#94203

So I will use those skills, with roughly those perks. Vampire from the start on master, getting the necromage perk later on (for obvious reasons). No fast travel and no shrouded gloves (to powerful). I'll join the db and thieves guild, not mages or companions.

So what race do people think suit the character and compliment the playstyle, heres my thoughts:

Altmer - good racial power, boost to magicka so more points can go into health/stamina, and a good boost to illusion and restoration. They are also the fastest race, complimenting the light armor assassins type character.

Imperial - more money through racial ability and a racial power that suits the vampire/illusion character. Boost to resto so it's easier to get to level 70.

Khajit - classic for a thief character, all the boosts are for skills I will use. But the night eye ability is useless as vampires get that anyway, the claws damage isn't useful later on considering I'm using one handed. They look the best as vamps IMO as they get huge fangs.

Argonian - good boost to skills and the water breathing ability is useful for evasion. Resist disease is useless as vamps have 100% immunity, they do look good as vamps though. One of the best racial powers too, making you near invincible for 60 seconds (90 seconds as a necro vamp). But I'm not a huge fan of argonians.

Dunmer - fire resistance is useful to counter the weakness, but I don't plan to be hit often (also alchemy can be used to help that area). Pretty useless racial power, but useful boosts to skills (apart from destro) for my play style.

Thoughts?

Race doesn't matter in the end, and really only helps you out in the beginning. However, if you're heading on that path where you need those stats to help you early on, then I'd highly recommend that you go for a Khajiit character for this build if you're really into the "cat burglar" type setting.

Edit: I played an Imperial Thief/Assassin and that worked out really well. So, if you're looking at attaining gold and becoming filthy rich faster, then I'd go for the imperial (a biased opinion though because I played this character, as you can see from my signature).

Dunmer for fire resist.

Skill boosts are extremely unimportant imo.

I've played Khajiit, Argonian and Bosmer on thief/assassin-style characters, and they work well. If you're playing a vampire, you may consider Dunmer for the fire resist.