What kind of kitchen do caterers need?

The best thing to do is approach a caterer for a quote and ask them to do a site visit at your venue to check out the catering facilities. They will then advise you if they need to bring any more equipment in and how much it will cost etc. To be honest, if it is a domestic kitchen with a small fridge and a normal oven with 4 hobs on it, I think they will probably need to bring in extra stuff unless you are only catering for a small number of people.

Well it depends what food you are having etc???

They won't be able to cook a roast for 100 people in 1 small domestic oven for example and they will need to safely store the food for evening buffet in a freezer/fridge.

That said if the caterers are local to your venue they may cook/prep off site and just bring on site to serve- although I personally would worry about the quality of the food if that was the case.