hello mate,
the tune is probably the most important thing in the list of stuff to get, the s300's are one of the best. if you are worried about driving it to the tuners then disconect the boost pipe to the throttle body then your car will drive like a n/a car.
there are a few things often over looked and that can result in serious failure. here is a few things i have learnt over the years of playing with b series engines,
SPARK PLUGS, i would recomend stepping down the heat range from 6 to 7 or maybe even 8, and make sure they are set at the correct gap for turbo charging, i have seen the hotter plugs melt before.
CATCH TANK, remember your engine will no longer create a vacum effct instead of sucking the oil vapours from your block and cylinder head it will pressurize it from the turbo
UPRATED IGNITION, if the spark isnt powerful enough it will missfire the minute you hit boost
INJECTORS, injector choice is very important, your injectors rely on fuel pressure aswell, your fuel pressure when under boost goes up with 1 for 1 on the PSI created by the turbo, for example static fuel pressure is 43psi and 10 psi of boost your fuel pressure will be 53psi, some injectors have a maximum pressure they can operate at, for example some injectors can only max out at 60psi.
these are just things i have learnt over the years with my own car and doing lots of reading up.
also treadstone performance does a lovely turbo kit for around £1600 delivered
hope this helps you out a bit