If you really want to keep it, garage it and project it. Strip it down and that way you can sort out all the problems, none of them seem major to correct (just time) and you have mechanic friends so it wont cost you and arm and a leg.
Mechanically, by the sounds of it the gearbox will need stripping down, which will cost £2-400 (unless your mates can do it. Handbrake shouldnt be a very expensive problem (cable etc). Your mates should be able to do the cam belt and all the rest.
At least the engine isnt knackered (I hope), the main problem seems that the electrics have been well and truly screwed around with and need sorting.
If you take it off the road, your mechanic mates can have a good look at it and sort out all the under the bonnet stuff for you while its off the road.
Then you can sort out the body work, hinges etc afterwards when under the bonnet is sound.
Personally, I wouldnt spend anymore cash on the car until your mate gives his honest opinion. Then you can cost it all up and see if its worth it. If your mates will do most of the work for you (cash in hand), then your mainly looking at the cost of bodywork which will be ~£200 / panel.
It always amazes me what condition people can get a car into, I saw some Mk3 before I bought mine that where in a right state. Bubbling on the body is pretty common.