How much food for a buffet?

Lunchtime - it's for Clara's christening. Service is at 9.30, should get back 11.15ish so will have tea, then have lunch at 1230 or so. Food will all be from Mr Waitrose ?

I'd really like to do a whole ham/beef with lots of breads but it makes life harder in terms of standing around to eat, so we'll probably have to stick with just finger foods.

Was thinking of sandwiches and filled rolls, sushi, quiche then the usual mini tartlets/samosas/canapes. Then dessert (cheesecakes and cakes I think) and cake with coffee.