This would depend how many times within the past 6 months you have entered Thailand if this is going to be your 1st and 2nd entry you should have no problem
Would depend if you plan to do 4 months in 1 period
60 days you get on arrival and can extend for 30 for another 30 days would need to cross the border land or flight and come back and that way you’d be granted another 60 days - you could use this option at 60 days to save doing a 30 day extension
You can visit 3 times in 6 months on the 30 day rule they have recently brought out the 60 days. So if you haven’t had a 60 day stamp it should start a fresh