Hi
Having done 2 now I would echo the above, I would also add that its easier to run brake lines, wiring, fuel lines etc on the new chassis BEFORE you fit it, also if you need the vehicle working quickly then stay focused on the chassis swap and DON'T get distracted doing unnecessary work while its easy to get access etc, unless you have time to spare then obviously it makes sense. Are you taking the body off insections or 1 piece, I have always used the lift in 1 piece option...
On a final note you MUST inform the DVLA of the chassis swap, they will want proof of purchase (receipt from marslands) and ideally proof of destruction of the old one, they may send you a new logbook or ask to inspect but its nothing to worry about, you don't need an IVA or anything just a quick check to make sure everythings kosher, then its all done nice and legally and theres no chance of future repercussions. I have just booked my VIC after my swap a few weeks ago and confirmed with the vehicle inspector that DVLA must be informed.
Mike
edit just found it here
linky
on the list of compulsory notifications
"replacing or modifying the chassis/monocoque bodyshell"