that first question is very vague
it depends on what boost youre running, what fuel system you have to cope with the new amount of compressed air being shoved into your plenum etc
also, what wheel sizes have you chosen for the hi flowed r33 turbo...have you put a t04 compressor cover on with a 56mm compressor wheel or a 52mm wheel. what AR is the compressor and turbine???? ....you see how vague the question is and how its impossible to give an accurate answer without providing more details.
youll need more fuel if youre gonna run more boost to take advantage of the new turbo. i wouldnt add extra injectors ever. its hard to get the ancillary injectors to atomize the fuel evenly throughout all cylinders which may leave a couple prone to detonation.
if youre changing the turbo, your best bet is to change the computer (fully programmable aftermarket ie. power FC for skyline, i used microtech for my VL) and the injectors at the same time for betting flowing ones (again, i used r33 GTR injectors because they are top feed like the VL and flow 440cc). by this stage, it all adds up.
by this stage youd want a higher flowing fuel pump and maybe an adjustable fuel pressure regulator.
the best way of finding someone to do the job is to ring various workshops and ask their opinion on the matter. some will only be too happy to help and provide great advice. then you decide who you felt most comfortable with and who gave the most honest advice and stick with them
goodluck!