Yep, on the brakes, as much as Godspeed brakes are warrantied for track work, it doesn't make them good at it. I have GS kit all round and don't get me wrong, it's fantastic day to day great early bite and feel but after 4-5 big stops at knockhill on Saturday, they may as well have been made of chocolate. Dreadful vibration. As a result it took a bit of a shine off the day but it just meant I had to cool them more.
Having been down the commonly perceived wrong route of POWER!! I still have fun at track days but in the corners I lack speed due to the standard suspension. You're doing the right thing sorting brakes and suspension first. Also, tyres are very important but if you go too track focused on them I'd be looking to baffle the sump and go for a swirl pot setup. These will ensure the oil stays where it needs to be and that the engine is not starved.
HTH