Okay someone can correct me if I'm wrong here.
1) There are options without all the mess.
2) Still don't understand why you aren't looking for the same engine as factory?
3) The gauges CAN work without using the mmdc. What I mean by that is some can be processed by the mmdc but others would not. The fuel, etc would all be controlled by it and then the oil pressure, temp, etc would all just be old school. Not perfect but its not a perfect boat either (no offense meant)
4) My merc doesn't use the factory in tank fuel setup. There is a master and a slave fuel pump that are mounted on the engine. I prefer this setup b/c of the obvious mc issues with pumps. Never have to worry about the 1/4 tank rule but the plumbing is not in depth and its a cable setup. NO THROTTLE by wire!