Terry, where have you been? (To others, Terry is good at this stuff

)
Just a comment on the levelling thing. Personally, I find levelling a tripod, as opposed to a top-pan platform, to be a rather tedious fiddle but maybe that's just me. Tripod flip-locks, as on Terry's M'frotto, are much easier for this than collar-locks (I have collars LOL).
And on the bubble levels fitted to many heads, I've tested maybe 30-40 of those those and about 50% are out if it's dead accuracy you're wanting. In practise a small error may not matter much, but the downside of levelling everything up in post processing is that in a wide pan like 180 degrees you will have to crop a lot off the top and bottom that loses considerable depth from the final image.