What would be the smallest mud boat that you could put dual engines on? This may be out in left field but if I select a boat just large enough for dual engines but only put one for now and the 2nd engine possibly later. If this was to happen would the larger boat to much for a single engine?

Technically you can throw duals on anything wide enough for the motors to bolt to the transom... That being said, there is some fairly straight line math on displacement that could help you understand the trade offs between bottom surface area and estimated draft.

In an 18' hull, I would be leary of anything narrower than 60".. 20' length, 54" would be my personal lower limit.. Not saying that you can't go smaller, or get clever with weight distribution.

Ok, if a single engine on a 1860 would be 25-27 mph with fish load for one, what would the estimated speed be with dual engines?