I'v just brought a mk5 escort that had been sittin under a tree for a couple of years n wasn't as bad as yours but was quite tatty in places, your engine bay brought back memories lol. like some ppl have said it depends on wot u wan't to spend on it n how much it means to you but if u already have the car u should strip everythink out take the bumpers off seat's, dash n carpet's out n as much trim as possible to have a proper look at things, just try n keep all the bolt's n fixing's in order cos it can be a nightmare if u can't remem witch bolt goes were, it'll also give u a chance to sort out wot need's replacing n can clean all the crap that has colected over time.

this is the time were if u don't do it right it'll bite u in the arse when u least expect it, so have a good look at the floor cons it's been sittin in a field for a while by the look's of it, n if its n e think like the mk4 escort's then there prone to rottin, i'm havin to sort my mk5 out atm even though when i came to buy it i missed all the rot, so give it a good poke with a screwdriver wherever it looks brown or tarnished aswell cos it could be rust lurkin behind mastic or thick underseal like i'v found. also like orion gav said check all the arches the sunroof, all in the engine bay basically every nook n cranny u can find, and n e were that look's rusty give it a scape with a screwdriver to see if it's eaten through, cos like all fords they rust from the inside out, just make sure n e good metal u scrape u spray with some sort of rust proofer, so u don't get a problem in the future.

all this will just let u no were u stand cos if it's too much work it might not be cost effective to sort out, n lookin for a better base to work with would be a better option, but this also depend's on wether gettin this car on the road means alot too you, cos n e think can be fixed at a price like with your fuel filler, i'v seen a repair panel for the mk5's so i'm sure if u have a search on the net u'll find one for your's or a mk4 escort one might be the same but not sure, n it'll involve just cuttin out the old part of the panel so the new repair panel can be welded in place, n is about the only option to stop the rust comin back, but the panel isn't alot n the price of havin it fitted depend's on wot u can get done yourself.

make sure you'v got a haynes manual aswell cos it'll be your bible when u get stuck with undoing somethink or takin out difficult part's of trim aswell as havin usefull wiring diagrams inside, n don't do n e think u think is too hard cos it'll usually end up costin more to put right than it would to just get it done properly in the first place, the rest is all just a learnin curve so hope you end up with a nice motor