BBK is not needed, but will save you money in the long term if you track a lot. The ESSEX AP Racing Sprint kit weighs 10lbs less a corner compared to stock....I would wait for the new AP Racing Radi-CAL caliper based kit they are designing though, especially if you need to save up funds..probably going to be a near $2.2k kit.
What is really needed up front on an FR-S that is to see regular track duty is:
1 - OIL COOLER....NEEDS TO BE YOUR TOP PRIORITY ON THIS CAR.
This car runs way friggen hot, the engine bay is fully enclosed, aero plates close off the bottom. Easy to see 230F daily commuting...I even had it hit over 240F on some canyon roads, which is when a computer failure started manifesting itself and the car went into limp mode. The clutch fluid needs to be bled twice as often as the brake fluid it seems...transmission gets HOT! Maybe if you are in a cold climate you can get away without an oil cooler, but the oil pressure runs on the low side with this car. You can chance not running an oil cooler...everybody I know who tracks says get on ASAP if it sees regular track duty. It's all about the oil pressure.
Being I'm about to get back on track soon since it's finally fully paid off, I'm about to make my own heat-exchanger based cooler (Laminova C43 core, 182mm length). That should keep the temperature in check enough and has better daily driver benefits along with having a very low pressure drop.
2 - Better brake pads and brake fluid.
The weak point of a stock 86 is the brake system... better pads suited for track and fluid will help it out, and adding brake cooling would be a good idea as well, but not totally necessary.
3 - Suitable tires in stock size for now... no need to over tire unless you have power level that requires it.
215/45-17 track orientated tires will be PLENTY of grip. An 86 is pretty light on its feet and doesn't really need big fat tires...big fat tires can be hard to get up to temp on a stock 86 and will really wreck the unsprung weight. A little more camber wouldn't hurt either, will need to get some camber bolts for that...camber is 0 and not adjustable stock.
That's all I would focus on for now, stock suspension doesn't need to be touched at all unless it is worn out enough and in need of replacement. Toyota/Subaru made an excellent chassis with an excellent suspension stock... it's not a stock miata. My plans once the stock suspension show it needs changing is just for strut and spring replacement, most likely Bilstein B06's and Racecomp Engineering Tarmac springs along with camber bolts.
One thing you might want to look into is how to do the 'pedal dance' or at a minimum, keep the systems 'off' by holding the button down until both the traction and stability indicators are lit ('off'). The systems are never off though with the button press and can re-engage. And 'Sport' mode is garbage on track when you have sticky rubber - will become very annoying, cutting power on you and the ABS system freaking out and pulsating the brake pedal for no good reason. When on track, keep the systems 'off' by either full button press or 'pedal dance' ('pedal dance' is the REAL off setting, and also disables EBFD which is kept on with full button depress.)
One last miscellaneous thing I would highly recommend is
solid Delrin steering rack bushings. The stock steering has a weird change/hesitation as you load up the suspension around mid turn in on sticky tires... the stock bushing are frankly garbage specced and allow slop and play and the rack to physically move around quite a bit. What is amazing is how good the stock car feels with those stock soft bushings that have way too much play. With solid bushings the slop and play is eliminated and everthing is very linear in response when turning the wheel, not linear'ish to logarithmic...and you get improved feel. Not an expensive mod either.