Its DS2's birthday party in Feb - he turns 4 and his guests are 3 and 4 (plus a few 6 year olds for good measure). We are doing it in the morning so muffins, cupcakes, some sandwiches, crisps, grapes, breadsticks, cucumber sticks, carrot and pepper slices plus cake.
I would expect parents to stay so definitely make enough for parents.
Mini pot of playdough and cutter plus piece of cake sounds fine IMO.
I wouldnt worry about it too much wannabe - its a kids party so all rules are relaxed. I'm doing the food we are doing for DS2's party as they are foods he likes (the weird child actually prefers raw veg to hot dogs and chips!).
You should probably also cater for children who are vegetarian/not allowed to eat things like sausages/have allergies (any religious issues?) - mini cheese sandwiches, humous and carrot sticks, mini cheddars, rice cakes all good options.
Hotdogs and chips perfect. It's a party. Parents not allowing junk food at a party should get over themselves. But if you are worried say on the invite that there will be hotdogs and chips and cake. That way any parent who has issue with it can decline invite or bring their own alternative.