I have a lot of experience with the PIC16F1455, and there are several good choices for a good USB bootloader. If you can get access to the ICSP pins (unique to the …1455).
I especially like Peter Lawrence’s work mentioned here…
And here’s a foray I made with this chip and Great Cow Basic, and good candidate for a next step beyond Scratch/Crumble…
Is there a schematic for the crumble posted any where?