Ultimately I would like the car to drive well / be rewarding, sound like thunder and have an honest 270 bhp, and more importantly I want to feel ever one of those ponies.
The GT V6 will be a great base to get all you have explained you want to have
When it comes to mods - all you have mentioned - exhaust, plenum, cams, remap all work together to bring out those extra hidden ponies. To be honest you will only unleash them properly with mentioned mods all done. Each item alone might give you 5hp - but all done together will give you an extra 5hp for free.
When it come to "feeling" the ponies you need to handling mods - Q2 / Quaife is the 1st MUST. Then again: stiffer ARB, shocks, springs, strut brace will each add to the handling, but together will be much more than each alone.
If you need to stage your upgrade path for your cash-flow to stay stable as you do them one-by-one my suggested sequence would be:
1. Exhaust pipe - decat /sport cat please - number one restriction of a) sound b) ponies.
2. Q2 / Quaife - now that you have some more ponies - handle them.
3. Plenum - OEM plenum was designed for 2.5L you have 3.2L - nuff said - the sound factor is upped as well
4. Time to add to the handling again: I would recommend an adjustable coil-over system: it is more than spring-and-shock combo while costing only a fraction more - most are height adjustable, so you don't have to guess what you want and then get stuck with it... oh and the front / rear height balance is not guaranteed - look at some rant threads.
5. Now that the car can breathe in better and breathe out better make the more air work for you - add GTA2 cams - GTA1 will be too little of an enhancement, but is still civil.
6. Now that you have all the performance thingies add the last pub-talk item before the remap (yes it will add power - I just had to throw that it there
7. Now make the enhancements work together - remap your bella
8. If adjusting the coilies still lacks a bit of that "on rails" cornering - add a strut brace and the ARB's
x. If at any time you start cooking your brakes by enjoying all that it you have a bit much - then do - in this order:
i) pads ii) fluid iii) braided hoses iv) slotted discs