yes you need better brakes ( small brakes + more power = Soon to be dead driver )
use a MR2 gearbox + halfshafts i believe
Motor alone is about 2 grand from most dismantlers
its also a good idea to upgrade the suspension + exhaust at the same - budget for that, Also what are you doing for intercooling - Gt4 Bonnet for the air to air topmount intercooler of the ST185 ? Frontmount ? Budget for these too.
Ask CeLiCa on this list - hes done this conversion
And your brothers car is a ST184 SX i think - not an St185