Hi TE
Have a look at CAP 453.. That has the guidance for A/G operators and as you will see it is a pretty minimal document.
Because of the enormous cost of providing an ATC service many fairly busy airfields prefer to hold on to an A/G service if they can.
You will find a huge variation in the type of calls depending on the airfield, varying from the seldom touched radio in the café at a quiet field to formal calls at larger sometimes multi runway fields where you may be sharing airspace with commercial traffic and the military.
Ask what to expect when you call for PPR. Once you understand what to expect you will be doing better than some professionals.
D.O.