I have the same Rollei kit from Freestyle. I mix all the chemicals at once. This gives you 500ml of developer which should be good for about ten rolls without having to increase development time (I'm on my 16th roll, but everything past ten is "noncritical" for me). I store the developer in a 500ml PET bottle, squeeze out the air, and keep it refrigerated between sessions. I do not prewet; my understanding was that this dilutes the developer slightly with each development. In that case, maybe increasing development time with each roll does become necessary. The trade-off is that you lose developer; after about five rolls you no longer have enough developer to do 120 in a Paterson tank.

I also go straight to bleach after developing (I'm curious now about PE's stop bath). I do add a rinse after the bleach and fix, which the instructions don't mention.