Oxygen is necessary to have a hot flame (and therefore a hot atmosphere throughout the kiln). By covering/plugging the peep holes completely, you are drastically limiting your temperature capacity in the kiln. If you need to adjust the drafting of the kiln, the most you should do is cover 1/2 of one or two peep holes. Never more than that.

When we raku at Bracker's (as seen in this slideshow), we fire all day long for a huge group of people, so we use a 100# cylinder and fire 6-8 cycles for each kiln setup (we usually have 3-5 kiln setups firing at the same time off separate tanks). Most people wouldn't do quite that much firing. We have two different sized burners available. The one you might see in the photos of us raku firing is the larger burner with a 500,000 BTU capacity and is appropriate for 40# or 50# cylinders and up. The other burner is a 100,000 BTU burner that is more appropriate for the smaller propane tanks like the 20# cylinders available at a hardware store (Home Depot, Lowes, etc) or convenience store. From our experiences, stay away from the Blue Rhino brand tanks - they're might be fine for the occasional backyard grill, but they aren't very good for raku firing. The small burner is also appropriate for 30# cylinders and occasionally 40# cylinders.

A local propane dealer (propane is also referred to as "LP" or liquid propane; search the yellow pages or online for propane and/or natural gas supply, grill-oriented businesses, or welding supply businesses) is a much better source for propane tanks and propane refills than the hardware or convenience stores that offer those tank exchange cages. Many times you can either rent or purchase a tank. When you own your own tank, you just need to take it in for refills and are only charged the cost for the amount of propane it takes to fill-up the tank. The propane dealer will also make sure that you have the correct safety valves and can help if you need a pressure regulator valve or, if necessary, a high altitude valve (usually not an issue unless you're on a mountain).

Either of the burners paired with the appropriately sized propane tank will work just as well as the other. The big difference is capacity. Is raku firing an occasional thing you do or is it a significant part of your work? If you plan to raku for a couple of hours once in a while, a 20#, 30#, or 40# cylinder with a 100,000 BTU burner is appropriate. If you raku frequently and/or it's inconvenient to get a propane refill, a 50# or 100# cylinder and the 500,000 BTU burner might be more suitable. The burners we sell are Red Dragon torches (they market them for burning weeds, among other things). Both of these burners are natural draft burners. It's NOT a forced-air burner (the air force would be likely to blow your pots over during this type of firing and is completely overkill for what a potter wants to accomplish in a raku firing).