You won’t need a PSV, but you will need to check the gross weight and your licence entitlement.
If you don’t have any additional qualifications and passed your test after 1997 you can only drive up to 3.5tonnes gross weight – this equates to a standard Transit or similar.
If you passed before 1997 you can drive up to 7.5t gross weight. Some buses may be below 7.5, a lot are significantly more.
I think you can have the vehicle reclassified by the DVLA to below 7.5t, so long as the unladen weight + everything you want to carry will be below this threshold…
Some of my friends have done the same thing. Drop me an email and I’ll see if they can give you a few pointers.
alaricdarmon@gmail.com