Don’t pay a penny until you are happy with the car in all regards not just how it looks.
check it has all the features you expected and you’ve also checked the car is suitable
Dont let them have your PIN number either.
It will save you a lot of hassle if you have to try and change it after you’ve paid.
As for Taxing the car all they should need is your award certificate and they can register it as disabled/tax exempt there is no charges involved.