Snook Slayer,
Welcome aboard!
I am far from an expert, but I just fumbled my way through rebuilding my transom and I also repainted my 222 inside and out. I am pleased with the results and learned alot along the way.
I prefer epoxy over polyester because: I am more familiar with it, It smells less, bonds better to cured polyester, is easy to mix, there alot of thickeners and additives you can mix with it for differant purposes. I used West System Epoxy and would recomend it. It is pricy at around $100.00 per gallon.
I considered using coosa board, the cost for my transom would be around $250.00 and there was no nearby outlet. I used AC plywood.
I used Interlux Perfection to paint inside and out. My original plan was to roll and tip off with a brush since I never spray painted. It took 1 1/2 gallon of 2 part epoxy primer, list price aroun $100.00 per gal. I used 5 qts of Perfection list price $80.00 per qt. Fortunatly I had a connection to get this stuff 1/2 price. I rolled and tipped the primer but did not like the results so I decided to spray the Perfection. I wish I had sprayed from the start!
Good luck with your rebuild, there alot of people on this site willing to help answer your questions!