
I told you DH would give you some stick but at the end of the day, LOADS of advice has been put in front of you.
You start following and you'll gain the respect of everyone.
Strut brace harnesses are stupid as everyone has said, I don't want to go into it as I'm sure I don't know every reason why, other then the fact of why you would want your seatbelts on the suspension turrets? Also from what I've been reading off DH, it's something to do with the angles? I assume you won't want to be putting pressure on the upright of the seat, if that gives way then I'd imagine at the wrong angle of belt then your back would too.
The fibreglass panels are a good idea but you need to make a priority list.
My main priorities would be in random order:
PROPER CAGE, do much research and listen to the track day "experts" here.
Suspension, coilovers are great but are they really better then a dedicated shock/spring kit with damper adjustments?
Brakes, how old is the car? Does it have the 280mm brakes? Would it be worth upgrading to the 288mm with DECENT pads, discs and fluid? Would it be worth going 312mm? How serious are you?
TYRES. No point in doing it all on budget tyres is there?
Then I'd look into some decent seats. Again, I've not got a great idea on these, ask the track boys.
Wheels, you want some nice, light wheels right?
THEN when you've got ALL that sorted, I'd look at lighter panels, you seem set on chassis work, before you've got a cage?

and the engine mods. Turbo if you're really into it maybe.
Your budget will depend how serious you are, as will how quick it will be.
Chuck a grand at it and you may have a bit of a toy.
Chuck 10 grand (at a complete guess) and you may have a bit of a weapon.