Darren,
Regarding bankroll, the 300BB number is just a guideline. If you're willing to drop down in limits when you lose signifcantly, you should avoid going broke assuming you are a winning player. 100BB downswings happen to everyone, so be prepared for them. You don't necessarily have to maintain a 300BB bankroll if you are disciplined enough to drop in limits when necessary.
Check this link for a discussion of bankroll along with links to other discussions include risk of ruin equations.
Good luck,
T