In theory it can be renewed for 5 years but only 3 in a single area of study like 3 years learning Thai then 2 years learning Muaythai/Chinese/cooking etc….
you could always purchase the 6 month METV and get 9 months out of each visa but no more than 60 days at a time in country, there is no official guideline on how many back to back METV’s you can purchase,
downside is that for each METV you want to apply for you have to travel to your passport holding country or a country you have an official govt registered residency or permanent residency in
you could get married or apply for a LTR visa if you have a medical issue apply for the medical visa….good luck
you only have to put it in if you stay overnight anywhere other than your home or place you stay in...if you have a hotel room and go for a visa run and go right back to the same hotel on the same day the hotel wont put in a new TM30 for you
Air arrival there is no official limit on how many times you can enter, however you will eventually run into an over zealous I/O who says otherwise….land border crossings it’s limited to 2 per calendar year 01 Jan - 31 Dec…if you get a visa and do a land border crossing it does not count against your 2 per calendar year….good luck