Flaps are easy to add to a model, 1 or 2 servos and a toggle switch with 2.4 Ghz
retracts can be a royal pain install, 98% to work to earn the 20 points for that option are done in the shop while you build the model. moving the toggle switch from up to down is easy while flying, making them work properly is the challenge.
You can build from a set of plans such as Brian Taylor or other designers, but check the outlines if you want to get the best static score possible. The biggest mistake people make is build the model and then find the documentation and 3-view. Pick the 3-view first and the documentation (photos) and build to match the 3-view and photos. modify the plans to match the 3-view and photos.
another option is to take a 3-view that is correct, get it enlarged at Kinkos/FedEx to the size you want and scratch build
If you don't want the hassle of retracts build a fixed gear model
Throttle only models are not at a disadvantage but if it's a single engine model you have a tough time filling in the options. but if you build a multi-engine model you can easily fill 5 options. Add flaps and you have 6 options. Look for options like bomb drop, open close doors, flaps and others that are just a servo.
there are many Kits out there that have been stretched or highly modified from the scale outline that almost make them cartoon scale. To be competitive you have to picky with the documentation, 3-view and the details on the model.
Fred