One or two
I chose two engines for the loop. There are pros and cons to each configuration, however economics isn't a big one. The engine/engines are pushing the same load, plowing the same amount of water, the same distance. It is the same work. If you move a cord of wood from one side of your yard to another. It doesn't matter if one, two, three people move the load. It doesn't change the amount of work. It just moves the load faster. The same is true of boats. Oil changes are one area where costs increase. I changed my own oil so the difference was oil and filter.
The hull for a single engine boat, trawler or not, tend to be configured as full displacement hulls with substantial keels. Full displacement hulls are most efficient at displacement speeds; add one extra knot beyond displacement and your fuel expense rises dramatically.
Propeller protection, which to me, is the biggest advantage of single engine trawlers. The loop has some very shallow areas, even in the marked channels. A single engine boat has no prop worries, whereas the dual engine needs to pay very close attention.
I did a loop and a half plus the Bahamas. Speed is the biggest advantage of dual engined boats. I think all two engine boats are semi-displacement and I can go incrementally faster without a large bump in fuel costs. At displacement speed I get 3.4 gallons per mile. For awhile, I have traveled with Mainships, Grand Banks, and a variety of full displacement boats.
The reason for I only traveled for awhile was the weather. I could adjust my speed to minimize the effects of weather and the trawlers couldn't. I sat for a week in Buffalo because of a storm. My, at the time, traveling buddies, on a Grand Banks spent 2 weeks because the waves were very annoying in their duration. I sped up to take them at a difference cadence. I had this same experience with others in Lake Huron, Lake Michigan, Gulf of Mexico and returning from the Bahamas.
There is no free lunch. When I go fast the fuel consumption drops to as little as a half a mile per gallon, but I didn't pay for an extra week at a marina in Buffalo.
As to size, we have a 40ft boat with a dinghy that hangs over about 4 feet. It is as large, as we want at the marinas we chose. Turning in the runway was tight at 44 ft. We recently talked to a couple who have a 54ft boat who love the size because they are put on the face docks.
If you expect any guests, you might look at two heads. It is hard for 4 people to operate out of one head. We had extra guests for about 6 weeks. Not a large amount but the second head was necessary for an enjoyable time.
Enjoy, there are no wrong answers. It is a great adventure and I hope you go for it.
Mike