You should keep questions on separate threads. That way people will see them faster. BUT.....
1) Trim Plate: I'm going to assume you have a Merc engine, since the Rotax boats didn't have an adjustable plate. (I will move this thread to the correct forum) There isn't any measurement. From the factory, it was flat with the intake. If you put it down, it will push the nose deeper into the water, at speed. So... adjust it as needed.
2) Intake Grate: That one is up to you. But, unless you are in shallow, rocky water... there isn't any reason to buy the stainless grate, since it will plug up faster. But, you want to get rid of the hydro-surge grate, since they are known to fail, and cause problems.
3) Sonar: What brand? BUT, generally... you want them no too far from the keel, to make sure it says in the water at full speed. Then, you want it flat to the water line. AND lastly... you want it to be slightly submerged when up on plane. BUT, that will be dictated by the brand, and style.