They are heavenly-looking seats.
As above, just get a decent car with the engine you want, they're the two biggest hurdles, the rest really is not hard, and you always were going to do a project vehicle. If you want it all done for you, then buy a Monaro, VXR8, or any number of other things with other badges, be it M, RS, VRS, AMG etc...
Don't let yoursef get too bogged down in the specifics. Some models have this, some don't etc...
other than pub bragging right about an LSD, I don't see the point really, I think even the most hardened car nut would have to admit that you're really not going to see the effect of a LSD on the road very much/often. And if you do feel the benefit, that person's perhaps driving a bit too close to the car's limits given that there are other people using said roads/pavements nearby.
Get something with a 6 cyl engine, ideally a manual if you don't want to faff of swapping that over. Make it what you want it to be, over a period of years, where funds allow.
Your question is 'which Omega to buy?' Thing is, if it's PFL/MFL it won't have rain sensing wipers, [probably] no HID, temp-adjustable heated seats, internal boot release. If it's a FL it won't look as nice (subjective), many models lose the sunroof, later V6 engines are strangled for emissions, lose the cable throttles, for UK buyers they pay higher tax on post 2001(I think) cars. But aguments over 'which model Omega is the best' have raged for many a year and are always ultimately flawed, because
everyone's Omega is the best, because the answer is always "mine." And rightly so. You make your Omega the best for
you.
If your criteria is 'highest spec, most kit and toys' then get a 2004 reg 3.2 Elite. But then a bloke with a rusty 1994 Elite will go "Awww, you don't have an air-conditioned glovebox and rear side window demist vents? Bless" it's the way things go.
But I appreciate you're just trying to get a feel for the model(s) and what's going to suit. Might sound daft, but how about buying yourself a few old brochures from ebay, they're often a couple of quid, plus postage, and it will give you a comprehensive idea of what's out there, get two or three from different years and you'll have a broad view of the range.