You will have to get those gasses from a wholesaler. Surely they will advise you on necessary licenses and so forth which probably vary from one juristiction to another. I like your plan to be available for sales during those times when I'm not at work. My daughter is a fireman. The best welding counterman in this area is a woman. You'll get no flak from me if you want to be a welder.
Bill
In Austin there is a few small (small) operations in addition to a really big national one, so apparentle it can be done, good luck, Dubliner
check out my company that i work for home page
www.welsco.com
cylinders will be your biggest investment if you buy or rent
lots of whole salers to buy supplies from.
what area are you in?