I have the T5 and the car it came out of, so that's a good starting point to go this way.
Not really when the car it comes out of is set up completely differently. You could say exactly the same thing about a 4 speed box from a K series Corolla.
Tailshaft wouldn't be too hard to get made up, as for the pedal box and clutch setup, you're on your own really (hence custom). Unless you're good at fabrication you'll be paying a pretty penny for these.
My advice if you want it easy - base the gearbox around the car, not the car around the gearbox. Unless you're going for a T56, there's not much advantage from a T5 setup and the work it required to fit it over a Getrag.
If you get a VT-VY wreck you get everything, flywheel (you can't use a T5 flywheel on an Ecotec unless it's from a VS S1), wiring loom, slave/master cylinders, pedal box, crossmember, everything bolts up and there's guaranteed to be no fitment issues. You also save the headache of buying everything separately which typically costs waaay more.
You'll also have to look into the ECU side of things as I'm not too familiar with the the VY and it's interchangeability with other models, VSS, or memcal retunes .