Other than the size limitation for a template/document, I know of no limitation.
Note that you can have building blocks in multiple templates. Those templates must be either stored in the Building Blocks folder or loaded as Global Templates.
Where can Building Blocks be stored?


I try to separate my building blocks by purpose. I do that by using:

1. separete templates
2. different galleries by type
3. different categories
4. useful, meaningful names (never the name assigned by Word as a default)

This makes it much easier to use them.


You can use custom galleries. You can assign keyboard shortcuts and QAT icons. (Shortcuts and icons should be stored in the same template that holds the building blocks.)

Build & Deploy Custom Building Block Galleries by Greg Maxey, MVP