Headunit spend about £200 on this, something decentish, dont just follow brand names, go for a good spec
speakers i would get some decent door pods (or make some), then an amp, then buy speakers
possibly Sub get a nice wheel arch box (or make one) as odds are you'll need the boot
polybushes all round as mentioned on here a few times, just do the front wishbones and only if they need replacing, dont do the rear beam or you're likely to throw yourself into a ditch when its wet
tints i did this on mine, had to remove the fronts due to police, but i do like them, a light smoke makes a massive difference when driving in the sun (4 days per year?)
Exhaust system i like the sound of an uprated exhaust, worthy investment, but just buy a backbox unless totally neccessary to replace the lot
strut brace personally wouldn't bother
panel filter not a bad investment, k&n's are guaranteed for ever and are cleanable
HT leads dont bother, total waste of time
chip not worth chipping an 8v, especially if you havent done other mods first, this would be the last thing to do
the budget is massive, i personally would get....
4x new tyres (uniroyal rainsports or eagle f1s) (£130-300)
headunit, amp, speakers, sub (in that order) (£400-600)
uprated shocks/springs (£150-600)
electric windows (£20-60)
air filter (£30-50)
backbox (£30-200)