Sounds like you've done more homework than the average "teach me to fly on this P51" beginner. Best of luck.

I hadn't done a specific engine comparison, but you're right, the Saito is about the same as the OS, and it's got a bit more HP. Of course people like to hot rod planes. You've probably already been to the Extreme Speed Prop Planes forum. I've just ordered a Lanier Shrike 10 kit. Specs say to use a .10 to .15 engine. I'm going to put an old OS .25 FSR and tuned pipe in it. Of course it's not a scale plane, I've been flying for quite some time, and making the necessary mods while building the kit don't scare me.

Monokote, or other coverings, are really pretty easy. The important part is to get some guidance, or read some of the good articles, before attempting it.