Personally, I wouldnt do anything to the car unless you are at a minimum intermediate level driver.
BMW brakes are notoriously great at first but will fade quickly...this was the case with every M3 I have owned and tracked....so this is not just a 335 issue.
Just go and have fun, that is the key!
If there was one upgrade I had to do it would be to upgrade to int. level brake pads like the Ferodo DS 2500's...but its a PITA to swap them all the time...although I have run them on and off the track they squeel.
If you have paddle shifters I would practice using them cause it will save you alot of time to down shift quickly while braking cause to heel toe on manual cars takes alot of practice and skill...thats not to say our paddle shifters are anything like SMG II or DCT cause it obviously isnt but better than nothing.