the answer is yes for brake fluid.I have change my brake fluid and my brake pads?
firstly the stock fluid is not high enough temp and you risk boil over
secondly brake fluid absorbs moisture overtime and the boiling point as such will decrease
thirdly you may be surprised, but after a few hundred miles can I can do a bleed and get some bubbles out
the club I go with mandates fluid be FLUSHED (not just bled) within a couple of weeks prior an event for safety purposes.
I'm glad everything worked out but it's a safety precaution to ensure your brakes will have the ability to be at their best. Nothing is as important as being able to stop. You do not want to be going 100mph, slam down on your brakes only to realize you aren't slowing down.
Diff and tranny fluid, I change after first 5k without track time simply because getting all the break-in shavings out is a cheap way to prolong their life but i wouldn't say it's absolutely necessary.