^^^^ There ya go Anthony. One of the GTST gurus I had in mind. I am sure if ask any of your questions here the guys that have actually built and raced GTST's will have some great info for you.
My personal view on brakes is get the best you can afford. I tend to sway towards bigger brakes as my view is they give you better feel and a better ability to modulate on the threshold of locking up. Added benefit is the resistance to fade and more stopping power, Some of the intense targa stages can really give your brakes a workout so they need to be decent. Have been down the path of upgrading standard brakes with braided lines, ducting, trick rotors and pads etc, but still got a better result out of ditching it all and putting 6 pot alcons on. No doubt there are upgrades like bolting later model brembos on to the earlier stuff that would be a good budget upgrade.
I sadly am not a nissan guy (would love a 34GTR but cant afford to race one) and am an imposter here, so take everything I say with a pinch of salt.
edit.... oh and re suspension, this is one area I learnt the hard way in that you can never spend enough on the right coilovers. Once you have had a taste of tarmac rally and see how hard your suspension works over the less than perfect roads, you can see why the fast guys spend big on the suspenders. Makes a big difference to feeling comfortable at high speed over the bumps, which will naturally lead to you being more comfortable to push harder. Again i am sure the guys here will be able to lay out the variously priced options.
At the end of the day we are all on budgets. You just try to build the best toy you can with the money you have.