there is information with links here:
http://www.buriramexpats.com/thai-visa/the information you're looking for is in the revenue office (
http://www.rd.go.th/publish/5998.0.html ) and you'll need a good lawyer and accounting to setup the company with all the paper work and legal side of it locked with contract.
lawyer in buriram that speaks english, don't think so,I do know a good lawyer in buriram but he do not speak english and I dont think he matches with your requirments and job you need to be done, keep up on your interest is also highly important,you need a lawyer you can deal with,not your partner/wife/gf only "tranlate" to you what "he say".
Maybe little english, not what you're looking for.
there is a good law firm providing all these services in Bangkok, they do have fair prices and most importantly they know the job.
Sunbelt Asia;
http://www.sunbeltasia.com/BTW, setup company need to have thai majority so I think the idea of 4 farang and 1 thai person for LTD not realistic.
good luck with it.