A couple of thoughts on your project.
one) Small propane furnaces / kilns are the least efficient way to fire any thing. For the temperature achieved the total BTU expense is inversely proportional to the volume heated per item. As a means of experimenting with the local clay I rather doubt you will find it satisfactory. Since you are a rural area you might find it better to experiment with wood/agricultural waste fired kilns. I would not dismiss the local potters so casually. In my experience with various crafts local knowledge will often trump academic knowledge. Making friends with local potters may teach you things about local conditions and materials that will speed you toward satisfactory results.
In addition my experience with small propane fired furnaces/kilns/forges, has shown that control problems increase as size decreases.
two) Commercial burners from companies like WARD Burners are by far the most practical way to build a kiln. Failing that there is a resource for building burners that I have not seen listed here before.
Gas Burners for Forges, Furnaces & Kilns
by Michael Porter copy right 2004
Published by SkipJack Press, Ocean Pines, MD Library of Congress # 2003115257
The contents of this book will short cut a lot of errors and futile effort, I wish it had been available 30 years ago.
It is possible to build a Kiln burner with very simple plumbing fixtures but making one with the necessary range of turn down (variation of BTU output ) is difficult and very difficult with out first class gas regulators.
You may want to read the extensive discussion of Kiln firing that appeared on this forum last week.