1.) What calculations regarding size of turbo, boost pressure etxc. do i need to do to work this out? i suppose i could carbon copy the guy in the gallery but id rather understand it first.
You'd get the compressor maps for various turbos and work out which one will be working efficiently at the boost pressure you want.. actually it's probably a lot more complicated than that when you take into account all the different things you can tweak on a turbo - compressor size, turbine size, blade cutback. But you want one that's working efficiently at your target pressure, you can work out turbine size by looking at something of similar capacity (so if you have one turbo per bank, 1.5L cars).
2.) MarksDTM mentioned the biggest challenge would be cooling. Is that cooling of the turbo or the charged air going in to the inlets?
Cooling of the coolant, the oil, the intake charge - all need thinking about. Cooling the turbo itself will pretty much take care of itself after that

3.) What about breather system? presumably that cant live in the now pressurised inlet manifold?
Correct, and/or it needs check valves adding in appropriate places.
4.) would i also simply drill a hole in the sump for my oil feed / return to the turbo?
For the return, yes. Just a hole (and spigot) in the sump
above the oil level. For the feed you need to tap into a pressurised oil feed somewhere; oil pressure sensor feed is a popular choice as long as it's post-filter.
5.) would i have to use exhaust gases from both manifolds or could i simply run a standard manifold on pass. side and my turbo manifold from drivers side?
Eh, the latter is a bodge (IMHO) and will lead to a very unbalanced engine.. you'd really want to either merge the manifolds and use one turbo or have one per bank. Both can be done, subject to packaging (which is tight on the Omega!)
6.) is there enough room for intercooler gubbins at the front? i presume so as its been done but would i have to make ''adaptions''
Dump the aircon and you gain some space.. or the windscreen washer tank and gain a ton of space (relocate it to a smaller tank)
7.) finally is this something i could achive on my own?
No disrespect but right now, probably not. Given time, yes, definitely. You'll need to do a lot of reading on turbocharging, learn to weld pretty decently etc etc.
Oh and to simplify things you might be better off just looking at crank driven centrifugal superchargers (Rotrex) - they're half a turbo, essentially, with the turbine side replaced by a belt drive. Much easier to package.