That depends on the aircraft type and the scale, of course. You can calculate it by dividing the size of the real aircraft (see Airliners.net aircraft data) by the scale. So for a 747-400 1:400 model this is 70.67m / 400 = 0.177 m = 17.7 cm.
Can I pick up a model from your warehouse?
No, we only sell through our website and we can't accept visitors in our warehouse.
I want to buy a model of type X and airline Y, can you get it/make it?
We do not make the models, we sell existing models of different brands (Herpa, GeminiJets, etc.). The brands decide what models they make. We always stock ALL new models of the brands we sell, if we don't have a model it just doesn't exist (or it is not available).
When will you receive model X
If we know, the info is on the website and the model can be pre-ordered. If this info is not on the website we don't know.