I waited until my sneak was really high and my pickpocket was up there a bit too. The fun thing about TG quests is trying to do them without violence. Killing anyone can do.

You can level up substantially by Pickpocketing everyone in town.

32+ for the strongest armor, 46+ for the strongest versions of the two blades you get. One of the blades is the strongest one handed weapon in terms of damage.

Just do it whenever you want to, i did the TG first (between level 10 and 30 overall) and i really enjoyed it. Yes the weapons and armour i gained arent super powerful for higher levels but they certainly made a big difference to me during the harder part of the game (around level 20-30 i found it difficult). I still use them from time to time but i can make better weapons now.

I got chillrend, i did TG in the 20s i think so i don't think it's that good, i'll have to check again. I know i don't use the nightingale bow or blade anymore. Boots yea.

My Chillrend does 22 dmg .. i guess i should have waited? oh well

is that your arm in your pic? nice tat dude.

Do the main quest like you normal would and when you finally arrive at Riften and Boromer (Can't remember his name) asks you to steal Madesi's ring. I recommend starting from there starting the thieves guild from there.