there is a basic step by step on using liquid mask here
http://www.rcsgraphicworx.co.uk/howto_liquidmask1.htm
as for spray cans, i don't use them so can't offer any advice apart from warm them up first to help with atomization of the paint.
you can buy mask from my site. i sell 8oz bottles if 16 is too much although they aren't up on the site yet so just give me a shout if you like. i have a few paint masks on the site also that i can adjust the size of to suit your needs or create new ones also.