FWIW,
1) 20 rolls will certainly give you consistency, but if you follow the suggestions in this thread, your intermediate rolls will be very, very similar with respect to how "developed" they are. What does vary in that time is mostly grain;
2) one of the advantages of X-Tol in a replenishment regime is that there is relatively little need to filter. I do it every once in a while when I pour the used working strength developer back into the storage bottle ;
3) I have never had trouble with foaming;
4) I have enjoyed excellent consistency over the years I have been using X-Tol replenished.
Prior to using X-Tol replenished, I used HC-110 replenished, which required a no longer available special purpose HC-110 replenisher. That required more care than X-Tol, but also gave good results.
In my experience, variation over time with replenished X-Tol is very gradual and small, tends to correct itself, and is probably related as much to variation in the types of negatives as anything. For example, if I have a run of dense negatives recording brightly lit subjects, after a few rolls it is a good idea to increase replenishment by 10-20 ml per roll for a bit.