it's only an issue if they cannot flow enough fuel, so at stage 1 the standard injectors are fine.

By doing as you say you are upgrading to stage 3 which is pointless as you stage you still want stage 1 power, yes, of course, as thats what mapping is, only the quanitity of fuel required is used, the precision can be further improved with the addition of C/L, which you may or may not have, if you have YBG (Green cam cover) then you have it.

Plus if you ever do decide I would get Siemens 55LB injectors, opposed to Bosch.

Martin