The skin is really where most of the flavor is and the inside is where there is a lot of water. The bigger they are the more the water. You can use them the same at least I always did but on some of the sites they pooh pooh the big guys. You can use the salt method to draw out some of the water if you are using slices or if you are grating then put it in a strainer and give it a squeeze before freezing and then again when you thaw.

I always leave the skin on for zucchini bread, some recipes you do some you don't. Depends on you I guess. You have to decide what you are going to use the zucchini for, I would probably just shred mine as mostly it would be going into breads and stuff. I don't do zucchini lasagna and the like. You would have to browse recipes and decide.