Thailand is full of people with criminal records from all sorts of countries. They make here like normal law abiding people, so little bans must be a joke to airlines.
You can buy a house, but the land on which it will be built will be either rented or leased. A work around is forming a company through which you could buy land. You will need a lawyer and the process is a bit challenging. But why do this? Just rent out your property in the UK and rent a house here. Much less problems and you get to keep your house which becomes a proper investment. That said, definitely spend 4-5 months here before making big life-changing decisions. Best of luck.
you won't have major issues if you acted within the law. Entering and staying in Thailand under various long-term visas isn't a problem. What they see disapprovingly are several back to back visa exemptions or simple tourist visas AND volunteer visas as several of these were bogus.