I once spent an evening with JCB. Very lovely man. He basically said Zappa worked bloody hard to attain genius but Don Vliet was a natural. However neither were exactly easy to work with. I think he still had a bit of resentment about the way the original Mothers were all dropped from the band.
When i met him he was supposed to be with the Grandmothers but they couldn't make it so the Muffin Men stepped in at the last minute IIRC (it was a long time ago in the Duchess in Leeds). The Muffin Men are indeed scousers and came out of the ashes of a fine band called The Wizards of Twiddly.
As for Zappa albums i suggest most stuff up to about 74 and then the odd later live ones. Live was where it was at really.