Sometimes it's a better deal to lease gas bottles than to buy them. Most any good welding gas supply place, like Airgas, will rent/lease the bottles. You pay a one time fee for the lease and then refills are cheap. If at any point in the future that the bottle exceeds the test date they replace it at no charge to you. If you buy the bottle, it's yours and if/when it requires retesting it will be at your expense.
As for welding outdoors; anything that will block the wind will work. Cardboard, plywood, and they actually sell portable wind and flash shields for that purpose.
Be careful with auto-darkening hoods. Keep the battery charged (most charge by solar) because if the bat goes dead while you're welding you'll get a face full of very bright light. Ask me how I know