I am remaking my thief for a couple different reasons, primarily being that I used a couple of the `cheats while I was getting used to the game, and I'm very disappointed that masks don't work with male characters due to beards.

Anyway, I was thinking about what my game plan would be, and then I suddenly realized I'm not too sure what to do, and I don't want to dive into the game and mess up.

-First, I'm aware at what the 'good' thief classes are, but other than starting stats, race is fairly useless, the only thing to consider is the passive. In these games I usually get a race that ISN'T very well suited for the ask, because if you're starting the game with 15 sneak/pickpocketing/lock picking, you're going to level up a lot quicker, and have more perks at your disposal. I was thinking, under this logic, the magic resist from Breton would be a great choice. Thoughts?

-Secondly, as for the thieves guild and TDBH, I'm wondering if its possible to join 'too soon'. The thieves guild I'm not worried about, I would either do it before the Golden Claw quest, or right after. However, TDBH provides some of the best armor in the game that is easily obtained. If I do the quest chain too quickly, would I be gimping myself on the opportunity to keep this armor for longer? I ASSUME the only real stat lost from doing it sooner is the armor value, and since thieves aren't SUPPOSED to get hit, I feel torn about the situation. Regardless, on my old thief I had the Guild's armor for when I wanted to steal stuffs, and when I actually quested I'd switch to TDBH.

Any advice is welcome, thanks!

Breton for Magic Resist
Nord for Frost Resist
Dunmer for Fire Resist

There's no leveled items from either the DBH or TG until practically the last quests, so join either of them at your leisure.

See here for info on leveled items; http://www.uesp.net/wiki/Skyrim:Leveled_Items
The Nightingale gear is the thieves guild rewards.

Thanks very much for the reply. I had another question, if you're still around. Would leveling Conjuration [via weaponry] be a decent idea to level up the character a little faster? I hear the conjured weapons are great early game, but fall short of crafted / enchanted bows late game.

I don't really know anything about the bound weapons in this game. I'm not sure anyone would be able to get the stats for them without the CK or some extensive testing so I've never used them myself.
One issue with them is the bound weapons only give you experience if you cast them in combat, which means if you get jumped unawares you're weaponless untill you get your cast of. They're also on a timer so you risk ending up unarmed mid fight and if you're not a mage you probably wont have the mana to cast again plus you're draining mana that could be used for healing.

Thanks again, you've been a huge help. :]

http://www.youtube.com/watch?v=yd2X8ciPEIA