Best place to look for final drive or ring and pinion would be either trd or richmond gear. I had weir in my ae86 but i dont know if they do frs brz stuff.
Lsd depends if you want a pure skid sled or grip driving. Grip a 1.5 way is better. A 2 way will lock on throttle lift too. Kinda sketchy if you doing high speed circuit stuff.
My ae86 had a weir spool so it was like how can i drive this WITHOUT it stepping out? The answer is who cares its a blast haha
But my s14 had a 1.5 way cusco and it got frustrating sometimes when linking turns, would try for a weight shift and it would just unlock, car regains grip at rear and flings me wherever. Got a vid on youtube of that and i went off course and hit a telephone pole that was laying there for some reason, at ebisu circuit no less!
Anyway, do some research before you pull the trigger on something thats going to determine a very large aspect of your cars characteristics and purpose.