Don't feel obliged to do the whole class. By next year your boy will have some idea of who his closer friends are, I've managed to get away with smaller sized parties all along - right now my DD2 in year 1 could only think of 5 she really wanted to invite. Fine by me as we always do parties at home (and no, we don't live in a mansion, just a small semi), my absolute maximum is 10 including birthday child.
Not sure about this whole class idea.thought of entertainers in village hall doing a pirate themed games etc. in Norfolk, any recommendations , been to so many soft zone parties. Thanks any ideas or advice welcome Ps party early next year so planning ahead