Hi Morning Jacket.
T2W is predominantly a European forum. Most of us based in London. UK prop firms dont really trade equities, its 99% futures only. But imagine business model is similar.
The deals depend on how profitable you are, how much money you have in your account. For an experienced trader with £10-20k in your account around 70% of net earnings fairly standard payout. Fewer and fewer places are giving out 80%+ splits these days, just no money in it for the prop firms. Unless you have £50k plus in your account and you are effectively 100% self backed.
In terms of margin/commissions it probably wouldnt really mean much as you trade equities and to be honest wouldnt know what is cheap or expensive I have never traded individual shares.