Interesting, a minimum wingspan limit this year. Those are going to be heavy models compared to a couple of years ago, since the high Cl(max) airfoils that have been popular are Reynolds restricted (min 200,000 for the 1223). That would mean a min chord of about 12" @ 25mph...and a min wing area of 1400 sq" (12"x10'). Bring out the composites folks!
That paper is cheating...it explains most of the hard parts about designing these models (at least for the report)
1) Planform is only one part of the equation, but it is important. The situation you describe leads to a wing that usually stalls with a nose-down pitch, which is fairly safe. Beware that the taper ratio doesn't put your max local Cl too far out towards the tips, however.
Stall behavior is very important for these models, since they are operating at highCl/high alpha most of the time. Any attempt to reduce the load on the pilot (not worrying about a spin, for ex) will be very valuable...and very appreciated by your pilot!
I have a spreadsheet that might be helpful if you want to play with planform. It's an extension of LiftRoll, among other things. Post an email address if you're interested.
2) Be careful with these measurements, and remember that engine performance will vary widely from place to place. Compensating the measurements was tricky for our team.
3) Winglets are more useful when your span or planform is restricted. The best winglet is a bit more wingspan!