Looks like a very doable project: lots of filling and fairing--time consuming. But probably hot huge expense--except the outboard.
As for a bracket: One 22 has been extend, and there was question about doing a bracket on that but I don't believe the project is finished. One of the 25's has a transom flotation extension, but the left the smash well--not getting fullest advantage of the extension. However, the transom in the 25, really needs the splash well. (at least in my 2003 boat). The boat is claimed to run well. Several of the 26 and 27 have had brackets/floatation added and do well.
If I was doing a bracket, I would do a full hull extension--the boats were originally designed for a light weight 70 hp 2 stroke engine. Keeping with the philosophy would be best if you added the bracket. It will change the steering geometry, there may be a little increase in speed, for the same HP...I probably would add knees at the clamp and keelson (and glass in a length of keelson inside of the boat to give more support to the new full height transom). Doing that you might want to move the fuel tanks up to each side under the gunnel. this would get more weight out of the back. but more costs for new tanks....
With your time frame, I would do the cosmetics, paint and power--enjoy this summer and then make a decision about the transom/bracket as a potential project next winter. However, if the transom has some water intrusion/delamination or rot--then go directly to the new full height transom, with the bracket.