hey mate, so firstly check out this video here > https://www.youtube.com/watch?v=UWcODnj2Ps8
Do not worry about the lay calculator. Use the DUTCHING calculators, like i do in the video at the bottom of http://www.thecashkings.com.au , and in that video above.
That commission is for when you are using the exchange, Betfair. That is more advanced stuff that you do not need to worry about at all for now.
I would focus on getting your bonus bets,and turning them over on EPL this weekend! Duplicate the EXACT process in those videos