Only from hearsay: a lot seems to have changed at LKVO Vodochody recently, and reports have been quite mixed. I would recommend you get in touch with the operator to get your information confirmed.
As for a stop enroute: I have only been there once, but have a good memory of EDBJ Jena - fuel available, nice restaurant, very able and helpful ATC staff.
Do not forget however that, departing from the UK, your first stop in Schengen needs to have immigration service, which seriously limits your options.
Would you have more info about the airshow? website? If it is at Kbely, as you seem to suggest, will that not seriously affect operations at nearby Letnany, if they aren't even completely disrupted?
[[edit: I should have looked before asking - it wasn't hard to find
www.efaprague.com/wp-content/uploads/EFA-Prague-2015-Brochure.pdf Looks like a continuation of the event I visited a couple of years ago at Przibram. Wonder why they moved elsewhere, it was a good location. Perhaps they found Kbely less hard to pronounce, or perhaps they value the ILS approach? ]]