Museums I think are much harder than houses. Because you want to display items, and it can be tough to do something that is attractive but also essentially a big repository for display cases. Miss Echo did a very lovely art gallery type house a while back that was really more like what you would find in real life (IE railings and such), and I wish I could find a picture of it.
If you have just tons of rares then it will be especially tough to avoid having a big box of a house. So you'll probably just have to suck it up and try to make it a very pretty, interesting box.
Without knowing more about your collection I really couldn't say what to do. While taking pics of all those museums I saw quite a few collections where the owners did their best to integrate their items into a natural setting and therefore avoid having too many display case type areas. So cooking/cookware type rares would go in a kitchen setting, outdoorsy rares like 2 story stats or plows would go in a garden setting, etc. I think rare armor/weapons and clothing is the hardest to display, since once you start collecting it you can end up with a lot of it. You can consolidate a little bit, for example by putting a vet robe/cloak collection in a gold box and sticking that in a bedroom setting.
Of course you may not want to do the house thing at all. In which case I'd count up all the rares you have and figure out how much area you need, then try to conserve space so you can get more creative with where you put walls and staircases.
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