bligh,
Twins or single
Galley wherever
Rocna or Delta
Those aren't keel shaking choices. Ya can't miss.
Actually the TS (twin single) decision does carry weight. It's actually not a TS matter it's a matter of how much overpowered do you want your boat to be and how underloaded you want to run. Since almost all trawler manufacturers used the same damned engine T or S. So your choice is 99% do you want a 120hp boat or a 240hp boat.
If you're a typical TF member you're probably much more concerned w fuel consumption than speed so if you ARE typical I'd recommend a single. Far less underloading. But if you aren't worried about burning 6 to 8 gph get a twin. The twin screw boat is by far the best arrangement.
Generally you should have more choices. Consider the GB 36.
A. Twins ... two 60hp engines or two 120hp engines
B. Single ... One 120hp engine or one 240hp engine.
In other words you should be able to chose how much power you want on the boat AND how many screws. If you get off running at 6 knots AND having the capability of going faster perhaps three screws would be best. On our 36GB that would be 3 40hp engines or 3 80hp engines. But ideally how many screws you have should be independent from how much power you have.
This post illustrates one of the huge advantages a custom build has. In the trawler market of the 70s. With the GB36 if you wanted a 120hp twin or a 240hp single you were just plain SOL.