Freedom Flight makes excellent kits. Like we've stated previously, design is not the main factor in this event - trimming and testing is. The main design variance is in flappers vs. non-flappers, and I personally don't think that trying to trim a flapper is the best idea for a team building their first glider. Weight shouldn't be an issue with any design, as an experienced modeler can build a glider of these dimensions down to 1.5 grams. My lightweight gliders are usually slightly over 2 grams and I don't have particularly extensive experience.
I've been casually flying gliders for a few years (Twice in SO) and haven't ever managed to build a functional flapper. Beyond the first glider for learning, though, feel free to experiment and try whatever. Just know that flappers are significantly more difficult to trim.
1 foot per second is an excellent sink rate, and probably near optimal. The next step would be to make fine adjustments to flap camber, et cetera for optimization. Sounds like you've heard this before and know what you're doing, though.