Without any of the things BAE asked for:
With a $300 starting BR, I would recommend at least 40 BI's for heads-up cash games (though you could get by with 30). For SnG's, I would actually personally say about the same.
Sadly, HU is about the highest variance NL Hold'em game there is, so you have to account for that.
I would personally recommend playing 6-max if you're familiar/comfortable playing it. 4-table 10NL playing standard TAG until you're around $700 then move up to 25NL and adjust accordingly.
Just a personal thing. If you're more comfortable playing heads-up, all the power to you. Best of luck! If you have any other questions, don't be afraid to ask!