uhh, consults giant map on wall, even though i don't read maps well...
Yep, as far as I understand, they switch locations on the different days, so you just stay at the one place and see them all.
As for the locations:
Chelmsford is in Essex, one of the counties surrounding London. I'm not sure how far it is outside London...maybe 45 minutes??
Staffordshire is in the midlands, westish I think, more towards Wales. I'm not sure exactly how far it is from London...I think about 3 hours though, maybe a bit less...
As for which is better, I've looked around a bit and I don't know a definitive answer. I'm having a friend who lives here ask around, so I'll let you know that. Basically, Weston Park (staff) is a bit larger from what I understand, but more open area and all. Chelmsford is less people, more condensed...I'm guessing Londoners tend to flock there, even though there are less people total allowed in the venue. It seems some people (just from looking at what people online have said) prefer Stafford...
If I find out anything more useful, I"ll let you know!