Ebay is a great place to buy second hand miniatures.
Miniatures by post is a good place to buy new warhammer it has a 20% discount on most games workshop products.
Unit fillers can help to stretch the models you have further, for example you could have a 40x60 base with a flagellant pulling a cart with a statue on it.
the empire Steam tank can be scratch built.
an empire mortar can be made out of the cannon set while still having the cannon!
