Hmm... if you went really Swish - - you could proably sort out rear electric windows using front electric window mechanisms, then connect all four windows to a full closure alarm system...
Firstly, delock the back doors at least, 5 doors are OK, but the handles are awful, and I'd paint the pillers inbetween the windows, so it's one long black shape down each side of the car. Looks like extended glass area.
I like a flushed tailgate, yeah. Make sure you do a proper job, though. It might be better to have a panel welded on their, and filler over that. I've never done a Mk2 tailgate.
Stick the numberplate on the lip of the bumper and put lights either side of it, or make a recess (cut away) some plastic of the bumper and stick the numberplate light in there, upside down.
If I were you, I'd go for 14s with a 50/55 profile tyre, 185 wide.
They'd probably just squeeze under the arches, and they'll suit the car's 5 door look.
Also think about meshing the front of the grille if you want to make it look pretty good. Uno Turbo front bumper & foglights (even if you don't hook them up - I like the look of em), try that, from a Mk2, and sand down, primer, wet & dry... basically, colour code.
I've never seen one REALLY WELL executed 5 door, in mk2 or mk1, although I've seen a few pretty good mk1s.
Make a breath of fresh air. =)
Post up a big picture of your car, side-on and I'll photoshop something for you.
Good luck mate.
Drag