Def stick to 2 courses. main and pudding.
I would do chilli and rice for one option Mince is always good and can stretch, say 1kg raw mince should feed 8 - 9 people, say 4 peppers, 6 onions, etc.
Veg option - pasta bake, salmon is nice but is very expensive.
and chicken curry/in tomato sauce with noodles or taglettie, mash is good too.
Jacket spuds are gross if left to go cold or reheated in microwave.
Pudding - go for huge sponge with custard? Those huge cream cakes you get from wholesales etc are discusting! Even through you are catering for many I dont think standards should slip. You want the backing of many and for people to come back.
My experience of caterers isnt very favourable, you have to pay a lot of money for decent food. Food safety, come on, surely with dishes that require good slow long cooking will be fine and we all managed well before the FSA started banging on! Majority of people have common sence and many people have food hygine cert.
Go direct to a good local butcher who will give you a deal and be cheeky saying that you'll advertise him at the event. Veg go direct to veg stall or wholesaler.
Do not use paper plates! either plastic (wilkinson do good deals) however you can hire which isnt that bad.