Re: First time boater
You don't need to reinforce to go from 20 to 25 IMO. However, there are only 2 things on this forum that are set in stone, and one is not to go over the plate rating on a boat (the exception being pure racing in controlled situations by knowledgeable boaters).
We have a 14' wide body Lowe jon boat at our hunt club. We ran it with a 20 or 25 (don't remember; probably 25) and found it was too much power for inexperienced boaters--we often turn the young boys loose in the small boats. With one person, even an adult, it was scary fast. When the motor died for other reasons we down-sized to a 15 which was a better fit. So consider who will be using it.
It is, however, typical to put a 3/8 " or so plywood pad to protect the aluminum, especially on the outside. Some use a thick rubber pad. Do not clamp onto lumber that size as it may split at the clamp and you lose your motor. And on that note, be sure to tie the motor to the boat (run a line from the motor down to the transom brace; leave 2' and tie your plug to it.)