Due to space limitation, as you say, I usually don't buy accessories like houses, windmill... but only smurfs. I store them in big plastic cupboards made for A4 documents (perfect size for smurf), not beautiful at all but 100 smurfs can be placed in one "drawer" and there are 10 tens drawer in one cupboard. That is a very high density, I know, but I have thousands of little blues ! (problem to look for any variation).
Recently, I did not have enough space so I removed the super smurfs and put them in boxes with name + Schleich number so that I can find them more easily (even if it is not practical and everything but easy to catch one box).
And I don't speak about the dozen of boxes with smurfs received but not inventory... everywhere in the flat...
How such little things can take so much space !