I don't sell parts. www.bulkpart.com
is who I get most of my rebuidl stuff from. I recommend CKPerformance for some specialty stuff.
I would start with a Th350 for learning purposes. CK will soon have a good rebuild/tech manual for the 200-4R, and bulkpart sells ATSG manuals.
You will need soem patience, home made tools, etc.
I use some easily made homemade tools.
3 liter pop bottle, section cut out makes a nice universal lip seal installer...
Cut the head off some bolts for guide/alignment studs.
I use a universal camshaft bearing (Lisle brand, same as all tool trucks) install/removal tool for trans bushings.
A flat piece of glass or tile can be used to do small light surfacing jobs. Or check for flatness.
You'll need some assorted snap ring pliers, feeler guage, 6" calipers, lip seal tools ( .010 feeler guage will also work, I like to have the looped wire one also, which can be made from some tubing and guitar string..).
Then a universal clutch drum compressor will also be handy, but if doing one trans 2 or 3 5-6" C-clamps can work, or other homemade compressor.