Here is what works for me:
1). Scrape all the old grease, oil, crud, etc off the tractor with old putty knives, pocket knives, wire brushes.
2). Power wash with Purple Power, or Simpel Green, or your favorite clenaer and hot water.,
3). Apply oven cleaner to the hard to get spots, scrape & wire brush again.
4). Power wash again with Purple Power, etc. and hot water.
5). Let dry a a day and then power wash with hot water
6). Get a bright light and over the tractor and make sure you got it clean.
7). If I blast I make sure to seal all openings, bearnings, put tape around shafts, etc to be sure media doesn't get in tractor.
8). I dismnount all tires, blast and paint rims etc. If you want to cut paint cost here, pain the inside of the rims with a cheaper paint. I choose not to, just use the same paint all the way throughout.
9). Blasting media-Aluminun oxide. Yes more expensive than sand however, in my opinion less dust and gentler on sheet metal.
Just what works for me in beautiful Nebraska. Your weather conditions make dictate different.