Funny you should ask. I bought a small freighter that ran from Dominica to St John, San Juan, Venezuela and a few other of the islands. Yup, buying it is the easy part, maintaining it and running it is a bit tougher. You better know how to weld, plumb, wire, etc. Oh, and finding crew for the delivery voyage home from the caribbean…never seems to be a problem!
Seriously- I guess the best advice is to start with a good hull and a good engine. Everything else can go on the 5 year plan. Best to line up the banker/insurance ahead of time.
Part of the problem is that if it is small enough to afford, it’s too small to run cargo. If it is big enough to carry a good load, and maintain schedules, you can’t afford it.
I still work mine, but play with it too- I have a big ol slow speed Cat that is very fuel efficient.
Good luck! Make sure you post here when you need crew!