You say technically you don't need IDP, but practically you do need. So what is wrong when embassies say you need IDP. They give you advice what you need. A lot of countries accept national licenses as long as it is clear for which categories they are, but they are never obliged to accept a national license without IDP.
visa exempt is for normal tourists which stay a short time. For longer times there is the Multi entry tourist visa which is more appropriate in his situation. You never know what kind of immigration officer you meet, but my experience at the immigration offices is they are always friendly and helpful as long as you also show you you want to cooperate and not try to misuse the system by getting as much free stamps as possible. I just left Hat Yai office 10 minutes ago after 90 day reporting. They were friendly as always, 90 day reporting was less than 5 minutes needed, finding place to park the car takes more time.
why should they not have the right to ask you for those foreign tax authority details? It is up to you if you give them, but if you not give them, they have the right to revoke your account.