1) At the FSDO is there a certain dress code or would t-shirt & shorts suffice?
As long as your genitals are somewhat covered, you should be fine.
(Remember this is Florida. Anything more than shorts, t-shirt and trainers will soon have you sweating like a pig.)
2) What should I bring to the FBO I am renting from for the BFR. Logbook, PPL, Medical, Proof of Insurance, Sectionals? Airport Directory? Headset Kneepad?? Fuel drainer?? Or what is the norm?
The BFR will probably serve a dual purpose. Of course it's a requirement to make your FAA license current, but it's also a rental checkout. And remember that the BFR is not just an hour in the air (minimum) but also an hour groundschool (minimum).
You you'll want to bring everything you normally need to bring to make the flight (with you as PIC) legal: License, medical, picture ID. You also need the stuff you practically need to make the flight happen: Sectionals, AF/D, kneepad, watch/timer, protractor/ruler, pen, sunglasses, headset, fuel drainer, checklists. And you might need some stuff to "survive" the ground school element. An extract of the FAR/AIM for instance (although you should know the relevent bits from memory of course.) Maybe a copy of the POH in case you get quizzed on that. And you'll want to bring your logbook so that the FBO can get an idea of your flying experience. (Plus of course it's your logbook where the instructor will eventually sign you off as having completed the BFR.)
In short, just bring your flight bag with everything in it you normally need for a flight at your home base, plus the US-specific stuff like sectionals, AF/D, FAR/AIM and you can't go very wrong.