Well i am Plans Motorsport through and through, they are also more local to you (Surrey).
All VXs have very safe geometry being 'Vauxhalls.' You want to go to someone like Plans for a fast road setup which will virtually eradicate all understeer. The difference is night/day and is pretty cheap.
After about 40k the dampers start to corrode quite badly. I replaced mine out of neccessity and opted for aftermarket coilovers. Nitron are aluminum and so won't rust, whereas Ohlins are just another level. You don't need suspension though... a geo is enough... but i as said i had to change them and had the happy side effects of better handling and a much better looks.
For remaps i would say Courtenay have the best rep, Thorney do it but they get a bit of stick now and then.