My Ek9 will eventually have the spare wheel well cut out and made flat, full weld in cage etc and there's definitely no return from that. But it's my car, if I upset somebody online for butchering an Ek9 that's their problem.
My particular bonnet isn't any lighter than the oem that came off to be honest, it's very solid in it construction. It doesn't sag or bend when it's up on the bonnet stay and doesn't wobble at speed what so ever.
I would suggest having a custom system made using larger silencers but still free flowing, a true 2.5" even 3" system can still provide the gains but be quiet enough for all race tracks.
The rack is the opposite end of the engine bay to the pump, it would be very difficult to get that wrong. The pump is a rotating part, if it fails it's going to make grumbly, grinding noises.
I bought a Godspeed cat back from the American eBay, full 3". The fitment wasent brilliant but a bit of fettling with hangers it was fine. That worked out around £350 with shipping I think.
The 76mm skunk systems are mega loud, you would struggle to get on track with it.