I believe it uses your entire balance to calculate your forced liquidation price, so say you have 100 BTC in your account and have it set to 10:1, if you limit yourself to trading with 250 BTC only, its exactly the same thing as having it set to 2.5:1. So really, you have any leverage you want up to 10:1, just limit your trades on your own.
Exactly. The leverage depends on trades only. Maintenance margin requirement has nothing to do with leverage either. The account leverage setting is just a upper limit that helps customers.