Regarding the Gaskets, I'm pretty sure your ok with the 200es set...
As far as tires go, you want a solid Knobby for the front and something beefy for the rear... Kenda and Carlisle sell nice affordable tires for ATC's
The forks will take more abuse than something with four wheels because the weight isn't distributed between 2 wheels (Imagine all that weight and abuse on one set of forks) The shocks weren't exactly built like they are today! And you have to keep in mind the age of your project!
As far as the frame issues go, you should give yourself a timeframe in which you try to find one locally and if your unable to, have one shipped! Give your replacement frame a good looking over (Stress cracks and bends) and have the thing Powder coated while it is bare (Powder coat is far more resistant to abuse than just a few coats of paint and well worth the extra cash!
I personally think a wheeler is worth restoration regardless of it's condition! These beasts are a dying breed and their existance depends on individuals like yourself that take the time to bring them back to life!
Good luck with your wheeler and don't hesitate to contact me with questions!
-BB
In the Garage:
1984 Honda Big Red 200es
1985 Honda 350x
1987 Honda 250x
(2) 1985 Yamaha 225's
2000 Yamaha Blaster 200cc
"If you got em, ride em!"