The inside of a pumpkin is pretty close to sterile, other then the pumpkin cells themselves, before you cut into it. So a surface sanitize should be fine.
I really doubt you could seal the top of the pumpkin well enough that a blow off tube would be needed.
6 gallons would be a lot of pumpkin. Maybe a good time to do a smaller scale recipe?
I haven't done it either, but it's also on my list.