Um, an 8" wheel is pretty massive. How much power are you rocking? I suspect that you'll lose more power than the extra grip is worth in friction running rubber that wide (to say nothing of unsprung mass in the wheel/tyre: this is bad because it's extra weight in the first place and also out of direct control from a suspension point of view) You'll also almost certainly need arch extensions.
From a track handling point of view, ride height only really becomes an issue when you're talking about extreme power levels (think F1/supercars etc...) where ground effects and aerodynamic eng of underside become very relevant to keeping the car from flipping. Assuming you're at a sensible sort of height then in this class rebound control is much more relevant (this would be assumed in the above nutjob scenarios to be taken care of as a matter of course). A certain amount of height is required or you risk bottoming out at speed on an uneven surface (shouldn't apply to track use).
My two pennies say that you will get much more performance for your cash with standard style spring and damper suspension than
coilovers which until you get to the megabuck range are much more about show'n'shine wicked low cars than they are about handling and performance. The ability to tune rebound rate is far more valuable to you on a track than the ability to tweak your ride height with a c spanner or whatever. This isn't to say that there aren't performance oriented
coilovers (they do fit them to Porsches etc, after all) but you spend a lot more cash to get them than you would on a decent set of regular dampers and springs. Bear in mind that the 'poundage' (ie, stiffness) of the springs is all important - this is what is actually doing the work of the suspension, the strut itself is called a 'damper' for a reason - it's there to tame the rebound and keep it all under control.
I think your first real think should be about getting some ARBs on there if you haven't already and either replace as many of your standard bushes/top mounts etc as you can with new OEM stock or uprated components (you would be surprised how much of an improvement even standard spec oem bushes make on an old car if you haven't tried it) and stick some decent tyres on the wheels you have and take it from there, possibly bolting a suspension kit in on the way.
Suj is dead right that bigger wheels aren't necessarily better. Unless you get insanely expensive superlight alloy jobs that would be wrecked by standard road use, bigger wheels are almost always heavier, in addition to needing bigger tyres (more weight) and causing more drag (wider tread=more friction).
Bigger rims makes it easier to run
lower profiles without messing up your gear ratios/clocks/geometry etc, and
lower profiles mean less 'tyre tuck under' - this is similar to body roll and makes a mess of your cornering precision.
Lower profiles generally cost more and ride harder. They aren't necessarily a good thing in seriously bad weather (which you aren't likely to have on a track anyway). For track use,
lower sidewall profile is a good thing. For comfort it is a seriously bad thing.
I see the point that 15x50 gives a wider choice of tyres, but I'm not sure it's relevant here as there are also very good tyres available in 16x45, and plenty of choice of real tyres in this size, just that 'budget' tyre at this sort of size is 50-60 quid and you can expect to see internet lists of around 75-100 quid a tyre. I generally get my Yokies around the £130 mark for a pair by shopping the tyre places in the north east around my Dads place. I tried this in Sheffield recently and gave up; all I could get around Sheff was no-name rubbish for real tyre money. I ended up getting tyres from a certain discount website that delivers to a certain *ahem* national chain of tyre fitters for no-extra charge installation and got good branded tyres for less than the rubbish the local guys wanted to flog me. It pays to
shop around, but everywhere is different is the lesson here.
Incorrect offset will certainly cause rub on full lock, but I have still heard of a car that had not changed its wheels/done anything silly with spaces or whatever that rubbed on one particular brand/model of tyre. The tyres were later swapped for a different brand/model and the issue never happened again before or after. Weird.
The bigger brakes are a good thing so long as you never plan to put smaller wheels than 15's on (because 14's will not clear the disc/caliper anymore).
The standard 15's and 16's are 6" wide, this will let you get to at least 205 which should be plenty without adding silly amounts of power so long as you pick decent sticky tyres (which won't last as long)
Your standard offset should be ET38. Varying from this will make getting geometry right harder and lead to issues like rub additionally.
The real
problem you're going to have is that what makes for a good track car is a huge pain (and extremely tiring) to use as a road car, precisely because it'll be so twitchy, harsh and follow every camber on the road.
If you can have two sets of wheels, a set of road wheels and a set of track wheels is a good thing as it means you can consider more exotic/expensive tyres for track that you wouldn't want to wear out in day to day driving. The track tyres are going to see way more scrub from extreme cornering forces anyway.
Not sure where I got the thing about Cordy track width from, happy to admit I'm totally wrong here; I'm obviously mixing
Ibiza's/Cordy's with something else, and I suspect it's old Peugeots, not that it matters.