Putting an engine in the nose does complicate things like where to put the bomb aimer. It's also going to make the interior of the aircraft more uncomfortable, which is like to be more problematic for bombers than fighters (the vast majority of which have nose-mounted engines) as the bombers, especially those designed in the 1930s, are going to be on much longer missions than fighters.
A number of other issues are really not significant. C/G issues crop up with all sorts of aircraft, with 0 or more engines. Quite often, when you see a conventional piston-prop aircraft with swept wings, it's a pretty sure sign somebody screwed up the c/g calculations (this is also the case with the Me262. The wing was swept because the c/g was miscalculated in the design process, not because of airspeed). A trimotor will have a more complex fuel system and will have a greater workload for the crew than will a twin, but less than would a four-engine aircraft. A four-engine aircraft will likely have more drag than a trimotor, both because of increased wetted area (those nacelles) and because of interference between the nacelles and the wing. More engines means more maintenance and will likely mean lower availability.