Thank you - I wanted to give an update - I have resolved my issue.
I was able to boot into single user mode and back up the config to a usb stick, and then I was able to manually fsck the drive to try to repair it. fsck said it worked and marked the filesystem clean, however after rebooting it kernel paniced with the same ffs_valloc error as before. So what I did is I replaced the msata drive and installed pfsense on that from a usb drive and since I had backed it up using the instructions provided in the link above, I was able to recover the same config easily.
So, thank you.