I want to organise a brilliant 40th in January in Edinburgh - any tips?

I'm expecting 100-150 people, I'd like to offer a buffet, and have a pay bar. For entertainment I'm thinking of ceilidh dancing - with a caller! - and either karaoke or a disco. I haven't got a lot of money, and I'll be organising it by myself. I've got no idea about costs, venues or anything... Help!