As said above, I would line work up first and make it clear to guys what you have. Also, more trucks and bodies. I tried that idea just locally the last few falls of wet weather during beans. I raise mostly small grains, and with the cows still grazing I had time to "kill" and money need to make. Got turned down by more people than I thought I would, and the hitch was, I have 3 semis, a grain cart, and only 2 drivers. That and the other reason was, I have a CIH 8010. most guys look at a custom cutter with a 10 year old combine and then turn and look for a cutter that has a fleet and brand new machines.
Ether way, only you can talk yourself in or out of the idea. Good Luck!!
I should mention, I do know a couple different guys that did just what you are wanting to do, bought old machines, kept them up got a reputation and by no means are they huge, but they are doing what they love and making a living out of it. They both hang around their area though, the one guy travels maybe 200 miles from home.