This biggest pain was the corners of the grilles. very difficult to wrap the vinyl round the corners without getting folds. I'd risk saying it's impossible to use one piece of vinyl for each grille, so with that in mind, I reckon it would be best to use one piece per straight side of each grille. Then one or two smaller pieces to do the corners.
Around the number plate it's obviously just one piece. I took my number plate off and let the vinyl overlap the recess for the 'plate.
I got the vinyl from a local hardware shop, and in retrospect, it's not the *best* I could've bought - it's a bit 'stiff' so it tends to fold/crease easily. I'd definitely recommend finding a signage company and buying some good quality outdoor vinyl.
tips:
I heard someone mention using a heat gun / hairdryer to soften the vinyl in those tight corners. I didn't try this, but definitely think it'd work.
Only remove as much of the backing as necessary - DON'T peel it all off and then try and apply a big peice - you'll get bubbles galore.
Depending on how much time (and patience) you have, I'd recommend taking off the grilles, as there are quite a few really tight areas that are tough to do neatly. but... if you're gonna go that far, you might as well rub them down and spray them
Dunno if anyone knows about removing the grilles on a pre-facelift but, on the facelift, it's not a quick job:
http://forums.fourtitude.com/zerothread?id=3631873