HLPlanner is free and so is FreePlanner (
www.freeplanner.org). If you can post here you must have access to a computer and an internet connection....
30-50m range on a BG that has an END of 30-50m... Do yourself a favour and do an adv nitrox & deco course and then do a mix course. Agency doesn't matter but find a decent insructor (which may or may not be your mates at the local BSAC club). This stuff is important, your life depends on it so please don't cut corners and try to do it on the cheap.