Not necessarily a 4 blade. A lower rake 3 blade with cup on the trailing edge not the tips works well. Old style OMC SST(Hard to find, but what I am using), There is a similar Merc prop and the Yamaha semi- cleaver should work well. Your stock prop is probably the SST II which lifts the bow(cupped tips) 18' SeaCraft CCs don't like those. Trim tabs are great, best $500 I've spent. As for the 4 blade, I'd love to try a Bay Pro III. The IIs are bow lifters.
My old 150 Johnson is 375lbs and thats pushing the limits for rough conditions. Plane @12, cruise 28 @ 3800 - 4000, WAO 42 @ 5500. Those numbers are when I'm fully overloaded, 3500lbs or so
