Burner size will depend on a couple of things. size of the smokehouse and anticipated smoking temp requirements.
with all due respect, to say that "No meed for 6' of burner, Just get - bar B Q burner & regulator or butane 1 or 2 burner stove." is ludicrous without more information.
With a small smoker, for example even an electric hot plate will provide enough heating ability to smoke/dry/cook as needed. I evidence this with an old, very small smoker i've had for years, an old Outers brand that uses an 1100 watt heating element. with about 4 cubic feet of space i can easily maintain temps of anywhere from 100 to 190 degrees. Plenty for things like jerky, sausages etc.
My larger smoker, which is around 20 cubic feet uses a small propane burner similar to a small gas stove burner, about 3 inches in diameter and will provide a 200 to 300 degree temp range. to get the temps lower i have to leave the door cracked open an inch or two.
What you are smoking will also determine how much burner you'll need. If doing larger cuts such as pork shoulders, briskets, or ribs, you will want to be able to start lower, around 200 degrees while applying smoke to your cuts, then gradually increase heat to around 275 gradually to a finished internal meat temp of anywhere between 175 and 195 depending on the type and cut of meat.
for smaller items, such as jerky, sausages, and the like, having the ability to start off with smoke, around 120 degrees while drying, and gradually increasing temps to around 160/170 degrees for finishing is important.
Note too, where needed, don't forget the curing salt, botulism is nothing to mess around with.
