there are a couple of items to check.
first of all, that bonnet is very likely a write off, and replacements are expensive new, and very hard to find (without being in just as bad state) used.
check the baulkhead very carefully, there is a seam on it, and rust bubbling there is a major issue, as you have to pull the engine to sort it properly. if allowed to spread it has a very detrimental effect on the rigidity of the body around the steering box, leading to cracking of the mounting holes in both the body and steering box - this is again a very big (huge) job to fix. Listen for a bang or thump through the steering and floor when turning lock to lock standing still
the GFX falling off may just be trim clips, but it may also be that the GFX have trapped water (common) and caused the sills to rust away where the clips are. this happens a LOT!!
the roof rust is a worry, there are many many water traps in the sail panel area (exactly where water likes to drain) by the time the floors appear rusty in this area its again likely too late, as there will be major corrosion if the internal structure.
the screen will need to come out to sort the screen surround, it will be broken in the process (well, 99.99999% of the time) so is again a pricey repair. budget at least £300
to repair the rust on that car, i'd expect to have to pay well over £1000 without paint, or more like £500 if you can find a decent used bonnet... but i bet you cant. (believe me, i tried)
panel availability isn't an issue.. shipping a 6 foot long panel weighing 150lbs from the states is!