There are 4 engine types available in the GT. The 1.9 16v JTD, the 1.8 JTS, the 2.0 JTS and the 3.2 V6 although I believe that it's very difficult to get a 3.2V6 in the UK after the 2006 models and i've only ever seen one 1.8 JTS. The JTD is the diesel and the latter are all petrol engines. Some models with the Alfas JTD engine are called JTDm, the m standing for multijet but AFAIK there is no difference in the engine in the JTD and JTDm, I think perhaps this was a marketing thing.
Aside from engines, there were initially 2 basic trim versions of the GT, the Veloce and the Lusso. The Veloce has Alfatex (suede-like) upholstery and the Lusso has leather and there are some other cosmetic differences like alloy wheel styles and sizes etc…
There are also certain "packs" that could be added to these models such as the Winter Pack which gave heated seats, heated headlamp washers etc.. as well as the standard options list where lots of toys could be added.
In addition to these there have been 3 Limited Edition models, The Blackline, The Cloverleaf and now the SE.
The Blackline was a "Limited Edition" (although they actually made more than they initially said they were going to, grrr) version of the GT and was essentially a GT Lusso with a choice of the 1.9 diesel, the 1.8 and the 2.0 engines. The Blackline was (naturally) only available in Carbonio Black but had a very good range of extras from the options list thrown onto it that were otherwise added-cost extras on the Veloce and Lusso models. It also had limited edition seats that you could only get in the Blackline (black with red stitching) and some Blackline decals inside and out.
The Cloverleaf was similar in that it was only available in certain colours (black, red, white and blue I think)and had a trim level that had a load of toys thrown in similar to the Blackline and some Cloverleaf branding. It was available in the 1.8, 2.0 and the 1.9 diesel variants again. However, in addition the JTD Cloverleaf has a “Sport” button. This button issues a command to the cars ECU which basically remaps to give the car more bhp, 170bhp rather than the standard 150bhp. The engine is the exact same unit as in the Blackline and earlier JTD(m) models but has the benefit of this “power” button which increases the power.
The SE is set to be the final version of the GT and is basically a magnetised GT driven through the parts bin. It has everything, xenons, rain sensing wipers, auto-lights etc.. and is only available in white EDIT: and red. But it’s a new model and is pretty pricey at the moment.
The Q2 is the brand name for a 2 Wheel Drive limited slip differential (there is also the Q4 for 4WD cars) and is an aftermarket part that can be fitted to all GTs. However, in certain Cloverleaf models it was fitted as standard from the factory. I have not personally driven a GT with the Q2 but I am told that if you drive one with it and one without it, you know straight away by how much tighter the car is in the corners.
To try and answer your remaining questions:
Was there any difference in really between a 2007 & 2008 GT? – The Veloce and Lusso models no. Although there is a difference in the early (2004) models and the later 2007 models but most are cosmetic (like shorter dashboard cowels). But 2007/2008 was when both the Blackline and Cloverleaf were introduced, there will be a big difference between a Veloce/Lusso and a limited edition model at this time in terms of what you get for your money in terms of extras. Sports button in the Cloverleaf aside, they are both fairly similar in terms of spec.
If I get one and drop a remap onto it, will the dealer actually notice when I return for services etc ( ie effecting the warrenty on purchasing from the dealer). Yes they will notice, usually when they take it for the short test drive after they’ve serviced it whether they will care at this point I don’t know.. It’s an interesting question because certain dealers offer a remap and say that it will not invalidate the warranty, yet I have read on here that Alfa UK take a dim view of this. The jury is still out I think.
Hope this helps.