Please note - I am not a mechanic or expert in anything.
Fair enough. Been a long time since I have test driven a car from a garage but over here I think it has been a long time back since you were allowed out in the car by yourself, unless you were known to the garage, far too much paperwork to allow that. I hope you done a few lower speed braking tests before the 90 to zero.
That is a good base but it does not usually cover the full maintenance service of car at 90,000 miles but perhaps yours does, if so you look for what has not been carried out, some items are not listed as part of services now but you might carry out if you want to have the car running really well particularly if you intend to drive it hard.
Best tuning you can do on the car is to make sure the whole car is fully serviced, maintained and repaired and that often is beyond the usual Dealership/garage full service history. You need a solid base to work and get improvements and upgrades from (those that are actually improvements and upgrades).
You do need to compare like with like, if you look a brand 'A', type/model 'B' discs usually their slotted and/or drilled discs are more expensive than their plain discs but you decide how much that price difference matters to you and how important the performance and looks/fashion are, good brakes are good brakes (and the tyres input to this).
Again the tyre itself is important - but this is track stuff in which case you would probably want different tyres to the ones for road use or be happy changing tyres a lot (lot) more frequently. I am all for spirited driving but public roads are just that and not race tracks. There is no law against how quick you get to the speed limit here, at least not yet, but such hard driving is very wearing on a vehicle. Though It is great to see some bloke with all the money to have a supercar and not being able to set a launch control so sits embarrassingly at a stop or just limps off 🤣 - this was off the public road.
I do not know how things go with your purchase but over here I can think of no reason why provided they are a standard size to the vehicle and wheels you would not be allowed to change to a set of better tyres within the 6 months and then as I put drive the car for that time to get used to it and discover what you want or needs changing or work done and this is the time to improve or upgrade, provided it keeps the overall balance of any system such as braking or suspension.
On of the very best tuning aids for a vehicle that is often overlooked, and is generally transferable to similar vehicles is driver training and I say this as a self-admitted (and confirmed by others) not particularly great driver. A trained driver can improve the handling of most cars they drive just by the way they drive it, on the road or track, I know I've been out on the public road with a couple and on tracks with a couple. As with a lot of things in life it is not what you have but how you use it and you do not need to flash it around when you are confident in its use - all this excludes me unfortunately. ☹️
Good luck, one day all this will seem to make more sense.