If you are getting a pressure blaster, then get at least a 100 pound sand capacity. I have gone thru about 1200 pounds of sand and am only about 1/2 way done with my 4140 HD Ind. It does have a more to do than just a regular farm tractor, but you will need to use a lot of sand to strip a tractor to bare clean metal.
The paint probably is a couple coats thick and then there is probably rust under everything, even the paint. The rust is 2-3x harder to get off than the paint.
If you have the air to run the blaster, figure on using 100 pounds in under 30 min. Oh, and get a GOOD blasting helmet with a nice large window and peel off protectors. And a good respirator is a must. Sand in the lungs turns to concrete and you can't hardly breath with a lung full of concrete!