If you're going to try retracts, go for the alfa retracts and try to mimic their installation into the Alfa kit as Dora suggests. The big issue with the FSK kit that might make retracts more problematic is that the spar is not in the best location. You won't really need flaps, and with the retracts (the alfa's are lighter than the robart and work better, btw) and rudder you might be pushing the weight.
The stock four-blade prop tends to flex at half-throttle and become less efficient. It certainly looks good, but as stuart wayne explained, a two blader might serve you better...
The Alfa website has some detailed pictures of the retract install that might prove helpful: