What agency can help me set up a company in Thailand for renting houses and obtaining a work permit?

Siam-Legal.com can help you in business setup, as long as you can meet the financial requirements for the work permit of at least bt2million in registered capital no matter what business structure you set the business up under. That is the deal breaker for many wanting a business they can get a long term visa and work permit with. But, Siam-Legal.com is very good, even in getting the required licensed Thai accountant, as accounting is a restricted occupation for Thais only, with many government filings requiring being signed off by a licensed accountant.