What level should I start HH at? I'm almost to level 12 and was planning on starting it at 15, but should I wait a few levels to start?

I went in at 15. It's as good as any. Good luck, and I hope you enjoy it as much as i did.

Well going in too early makes the enemies have less powerfull and expensive (money money money ) weapons so I prefer going in at 20+ just to scrounge up good weapons.

Money's not a problem, I have around 10,000 caps.