Well there are two downsides to doing the survey first. 1. You have to pay for it. 2. There is no "standstill" arrangement. Until you sign the P&S, another buyer could come along and grab the boat.
I am happy to give the seller a copy of the survey whether I choose to make an offer or not.
As for the surveyor, of course he will tell you about other boats. He works for you, the buyer, not the seller. Also, I look for a surveyor who is familiar with the model in which I am interested and has done recent surveys of that model.
I used this procedure in two cases. In the first, a boat in NC, the surveyor told me that at some point the cabin had been full of water, even though they had disguised it nicely. I did not make an offer. Several months later the surveyor told me that the next boat in which I was interested was in "cherry" condition. So I made an offer that was 12% below asking (a good offer in today's market) and it was accepted immediately. The only negotiating was what equipment would be included in the boat i.e. the inflatable. I got that too, even it was not mentioned in the listing.
IMHO instead of trying to learn how to be a surveyor, a buyer should spend his or her time very carefully going over the listing and making sure that everything you want is included. What about the inflatable, the outoard, the oars? Galley equiment? Fenders? The flat scxreen TV? Extra sails? Map chips for the chartplotter? Engine spares? Let your sureveyor deal with structural or mechanical issues.