NEW PROP QUESTION

i am in the process of buying a new prop and was hoping for some input. for those of you that don't know, don't care or forgot i have an 88' 18' cc with a 96' merc 125. the current prop has no #'s stamped on it anywhere so i have no idea what size prop i am running now. top speed now is 32mph with 2 men and a full tank of fuel. i normally run about 5000-5200 rpms but wot is 5800. should i go three or four blade? stainless or aluminum? ??? thanks in advance for your input ;D