they have exercise areas, but Lumpini park is the only park with a free weights area that pro Thai bodybuilders work out at. It's pretty famous in that respect. The rest don't have free weights, for power lifting workouts.
The best bodybuilding location is the weight training area at Lumpini park in Bangkok, and it is free to use. It is quite popular for those serious about bodybuilding.
As far as a visa get a multi-entry tourist visa, the METV. This is good for 6 months, and during those 6 months you get a 60 day entry stamp each time you leave, and immediately return to Thailand, and each entry can be extended for 30 days. With the correct timing you can stay almost 9 full months in Thailand, with simply leaving and returning just twice, and getting the 30 day extensions. Leave and return once your last entry expires, and you can stay almost 12 full months. That is the least hassle visa, and way to stay.
It sounds like you applied for a multi-entry tourist visa, METV, not a non-O visa. The METV is good for 6 months from the time it is issued, and you get a 60 day entry stamp every time you enter Thailand during those 6 months, and can extend each time for 30 more days. None of the non-O visas do you get a regular 6 months entry stamp with.
Put five years, but it determines on the consulate/embassy you use. Some people that listed under 180 days were given multi-entry tourist visas instead.
You personally do not do a TM30. Wherever you are staying does, and is required to file one within 24 hours of you arriving. If wherever you stay doesn't file one then they are breaking the law. Again you personally do not file one, unless of course you own the condo you live in
without exact details, no I can not help you, and no one else can either. Like I said before, everything is based on what your attending doctor wrote, not what you say.