Private plate value, and change of tax class

[Davi]

I've been offered a vehicle by a friend which is of interest, just not sure on two things:

Firstly, it's got a private plate which they want to sell separately. Where is a good place to get it valued / sold and what happens to the car sans plate?

Secondly, it's currently taxed as an ambulance, which it won't be if I buy it. Is it any rigmarole to change to PLG?

Ta muchly