Another tip is to design the icons such that they can be placed on non-white backgrounds. For example, your elevator icons are transparent in the middle, and would not be readable if placed on top of a green-colored room, for instance.
There is a trick to make the icons smaller, which involves adding some "space" around the icon when exporting them.
Our rule-of-thumb is to have icons designed as 34x34 in a 50x50 box, and then adjusting individually as necessary. That should result in around 16% whitespace on each side of the icon.
The more "padding" you add, the smaller it will look in the final maps.
Attached an illustration showing the difference: