Too many engines? Say it ain't so. Sounds like a state of mind problem... Perhaps it's not too many engines, but too few planes? Aside from overlapping purposes I don't see how the problem you're trying to avoid really exists. It's not like you can build two identical planes, and use two identical engines, props, venturis, etc. Every plane and setup is different, it doesn't matter if the engines are the same if you have 5 different planes you're likely going to find that 5 different prop/venturi/tank setups will give you the best results. The setup is going to be tailored to the plane.
At current I run a wide range of different engines on a regular basis. It'd be impossible to remember all the details, but the one that really is most important is remembering which plane/engine requires how much fuel to complete it's pattern. The rest of the details stay set for long periods of time and don't seem to be all that relevant. I've started logging all my flights, so I can keep notes of all changes I make and the results. If nothing else when I can't remember if I need 2.5 or 3.5 ounces of fuel, I can look in the book and see what it was last time.