A few weeks ago I would of said get an agent but due to all the 'bullies' on here saying do it yourself I recently did my own retirement visa and saved myself 20,000 Baht , take it one step at a time and don't stress, immigration are very helpful here .... Oh and thanks 'Bullies' 🙂
Yes you can buy a house and lease the land from your Thai Wife for a nominal fee, Get yourself a good Lawyer and make sure you are well covered in the event anything should happen to her, ie the Family can not sell or mortgage the land and must continue to give you full use of it as per lease contract.