Looks good for the price.
lemonnobby1 isn't quite correct. The hub ball joints can be replaced, although you'll have to go to Renault Sport not your local dealer for the part (dealers will only sell the complete assembly). I believe they are roughly £70 + someone to fit.
Front brakes aren't expensive at all, I run Pagid discs and pads on mine, a full front set up can be had for not much more than £100. If you want Brembo then talk to G 172 off the forum. The rears can be a little more expensive due to the bearings and ABS rings, they'll probably set you back around £200.
The seat can be repaired by Steve @ R-Sport cars for a very good price (£130ish)
Not sure where you stand on the belts. If you have proof of the engine change and the date then fair enough, if not then the belt is overdue.
So, if the belt isn't due then £500(ish) will sort all the listed problems, if the belts want doing then double that figure. So, if belts are ok, bid them £4k and see where you get, if belts want doing then I'd be wanting that for £3,700 to be honest.