thought i would answer the four questions i posted some time ago and got no response so i researched them myself...1). the good folks at shell oil said to always use midgrade fuel. midgrade contains additives the other two grades do not have. 2). sea foam, quickleen or power tune, in that order. 3). a four blade on the 16' fishing boat will perform better than a three blade and the difference in speed is not noticable and it does not make a difference if the outboard is a two stroke or four stroke or what manufacturer. 4). installing the 20hp carb will provide enough of a boost to make it worthwhile...only a 20hp will run like a 20hp but it will run like an 18hp. And if you can't or won't get out and burn some of that $4.00 plus gas then you deserve to sit at home and play video games with your fat kids.
I apologise if we didn't read your mind for the other three . . . 
