Actually harvesting is a mere 5% of the groundwork. You must be a politician, mother, father, manager, mechanic, psychologist, rigger, welder, mechanical engineer, electrical engineer, magician, and weather lucky. The expenses are murder ... fuel, tires, oil, parts, insurance, wages, meals, interest, lodging, fees, permits, and 1000 more. You need support equipment, service truck, pumps, tanks, welder, torch, fire extinguishers, compressors, tools, parts, roller chain, sickles, spare tires, oil, filters, bearings, springs, combine trailers, header trailers, pickups, trailer house, and 1000 more. You must be 10 places at once. You must not let your help ruin your reputation. You must watch like a hawk for unsafe situations. You must treat your customers crop as if it was your own. You can't back over augers, exit quonset huts with the bed up, turn too short and knock down light poles, leave truck stops and knock down signs, break the law, have your help break the law, go too fast, go too slow, be broke down, have drivers get lost, back into the farmers new pickup, and 1000 other things. You must be able to convince strangers you are the man for the job. You must pay everyone before moving on. Again ... don't be a fool.
But ... if you are ridiculously tenacious, fearless, not affected by stress, don't mind debt, and damned determined, go for it.
Congratulations you have basically described a farmer.
Series 3 and later wasn't that bad, and good part about them(compared to an R) is they are cheap and somewhat plentiful, so you could buy a few spares.
Comment not connected to this quote: I guess a way to start out(if you farm as it is or something) try local work first. Worst case you're 30 miles from home and you break down. 1/2 hour later you've went home and back and are in the process of fixing or are running again.