Hi guys, thanks for the info! really helpful knowing you park up next to where you camp, that makes life nice and easy

We don't have tickets yet and it's sold out, the only place I can see them for sale at a good price is Viagogo. Will that be ok? (I'm guessing we won't see the tickets until close to the event).
We're coming from England so plan to arrive late on the 3rd Aug hence wondering how much space will be left. I don't expect anyone can answer that, you have to wait and see.
Are there electric cables in the field for a cooler/music or best to run it off the car battery?
Viagogo? A little overpriced, no?

Well, usually from June on, prices will start to fall again. Since tickets are not personalized anymore, reselling them is now easier. And honest fans reselling theirs will usually not charge you more than the original price. But if you don't want to wait, who are we to stop you? It's only that we wouldn't recommend it.
Regarding the space, don't worry. There's always enough room for everyone. You don't need to cram up closer because you arrive later than anybody else.
About power, there are no cables at all. The only outlets are in the camper park, as said, and there are outlets at certain reserved spaces for campers. No cables ANYWHERE else. Whoever brings devices has to power them with their mobile generators. I would not recommend powering them with your car's battery. You don't want to drain it being dead when you want to leave.
You may bring generators of up to abt. 2HP, although there are lunatics who bring much bigger ones.
Edit: grounds are open from Monday Aug 1st. There's no bands playing on Mon and Tue, but people are already camping there. But beware, there's an extra fee if you arrive earlier than Wednesday 3rd! 20,-€ per person on Tuesday before 8PM, 30,-€ per person if you arrive on Monday!
Space won't be a major problem as you describe it. May be a little packed but still possible no matter what. Have fun!