Sounds like a good deal Rusty! However I would try to get the dealer to throw a new water pump impeller in it as part of the deal, since it's been sitting for ~6 years without turning, so the rubber has probably taken a set. Otherwise it might be susceptible to an impeller arm breaking off at pretty low hours!
Whatever prop you pick for that motor, the
optimum RPM for it is 5600-5700, so make sure you're in that range with the load you normally carry. (I prefer being at the top of the range or a bit over, as margin in the event you occasionally happen to carry a heavier than normal load.) BTW, check out that E-TEC owners forum . . . it's much like CSC, with tons of useful info from some very savvy tech's! Those V-4's love to rev so better to be above that range than below it. Also make sure you use an accurate digital tach like I-Command that ties in to engine computer, not some analog tach, as they are notoriously inaccurate! Before you start fooling with props, make sure the motor height is correct, with the AV plate on top of solid water, clearly visible when up on plane with motor trimmed out as far as possible. Most dealers mount them too low, causing extra drag and loss of top speed. I'd start out with a 3B prop for best efficiency, probably a 15" pitch for heavy load, but if your min planing speed is too high (all the Moesly designed hulls will plane at about 12 mph with the motors they were designed for, i.e. about 300 lbs or less for the 20). If min planing speed is too high, you can try a 4B prop which will add more stern lift and/or a fin on the AV plate.
I'd also run nothing but the XD-100 full synthetic oil; the engine computer comes set for TCW-3 oil, but the dealer can set it to run XD-100 only, where it will use less oil and burn so clean that you'll never have to worry about doing a decarb on it! My local dealer sells it in bulk for about $35/gal, if you bring your own jug. It's expensive but you won't use much on a rig that can get 5 mpg!