First the good news-be quick and get a big discount-even tough its not FRI here anymore.
Next 2: except for from B onward to PL (1/day direct Krakow, more connections via Poznan or Warszawa)-plus onward from Krk-you do not need any RES-its only optional. You can just do that str8 after arrival in those cities, thus avoiding all the online troubles and no, these trains are not booked solid weeks ahead.
The connection Pr->back to AMS is not that quick-you may also look into open jaw airtickets-go to AMS-fly back US from PRG. Often cost the same. But as global pass is MIN 4 days-it will not reduce outlay.
For untill around march/apr you can find train times on bahn.com= German railways, these will not change very much for later on. There are also NO really feasible overnighttrains anyway along this routing for now, though you could if really wished, use the NightJet Wien-Linz-AMS and get to some point of its trip from Prg. Will not really save that much time.
Now the tricky point: will it save-maybe/perhaps/canbe. Then you compare with the lower advance prices-which also means: no show-money gone. Will depend a great lot on when and how long advance and also your age-if you get discount on pass. First 2 rides via bahn.com, 3d via pkp-intercity-last-in this case better fly-easyjet or transavia, unless you want to see B->AMS also return-there are also other slower ways-more changes, via other parts of DE..