Sorry to hear this one wasn't top shelf. Crumbly and bitter does sound like it was over acidified, and bitterness could be too much rennet (which would fit with the fast floc), and/or too much starter (which would change your acidity curve and can result in faster flocs as well).
Check out some of the caerphilly makes that are around. There's one that I quite like which involves cheddaring the curds, and there are some other procedures which don't have that. Try both as the results are good either way, but see which one you prefer. This won't end up like a cheddar, but it is ready in 3 or 4 weeks, so you can tweak your makes quickly.
Also, if you're willing to age one out 4 to 6 months, have a look for my 3rd Wensleydale thread. That produced the best cheddar type cheese I've ever made, and by far the best. I'm going to try and reproduce it myself, but on the assumption that the procedure is robust and stable, I highly recommend it. It is a fairly long make procedure, but it is worth it in the end.