the law is, for that make of car, you can go 2 inches larger than the factory released on that entire model..... so, all vt.
i am pretty sure 17" was the largest rim from factory avaliable, so therefore 19" would be the largest size you can have on a vt legally. (unless i am wrong and there where factory 18" rims for vt)
my advice would be to keep away from any obvious mods like exhaust, extreme lowering (keep it legal) or the likes, as that kind of thing attracts the coppers. go for less obvious modifications, and who will know if you dont tell them
Pretty sure that Rim law is gone now, otherwise every person with 20"s or 22"s would be pulled over.
As for the laws, Yep P platers can't have anything to do with the engine, I.E The exhaust, insulators + spacers, extractors.
That being said, I have Pacemaker Extractors with 2 and half inch catback, which is fairly loud but I've never been done for it and I've been pulled over twice.
But, I probably get away with it because i have factory tint and the car is standard height.. Which is obviously going to be changed but not sure.
I've ran around with the exhaust with stockies on the back and 18" SS-SV6 rims on the front with no troubles, even though i had a legitimate excuse, it still gets you pulled over.
What you could get away with and which is bang for your buck would be High ratio Roller rockers, Diff gears + the manifold insulators + spacer.
Just don't make yourself look like every other p plater and you'll be fine, anything you want to do to your car i'll garentee you won't be aloud to have, but you'll do it anyway.
Remember the consequences, usually you only get ####ed up the ass if you're being a tool anyway, which in that case you deserve it.