That's a lot of money for very little gain. I'm as pro-NA and anti-FI as you are, but even I wouldn't dream of spending £8K on NA on the Zed, it's simply not worth it IMHO.
If you're fitting it all yourself and that's half the fun then actually, I'd get that. Doesn't sound like you are though, unless I'm wrong. You could buy a whole other car for that kind of money, and as a second car it wouldn't need to be remotely practical, and it would be a hell of a lot more fun. Or you could spend £4K on driver training and see a much more positive result in terms of pace you can carry, which would then set you up for life. Or that's a lot of tyres and trackdays!
I mean, kudos to you and I wish you well in your project, but I thought I'd give you a sanity check from someone who's not going to just batter you with the "Just go FI!" line. If you're going to do it, then at least do something a bit unique, like ITBs which would be amazing.