I would recommend you consider some other options besides building blocks if you have such an enormous number of sections. I don't think putting 2000 building blocks into a list is going to be a sensible workflow. The heading hierarchy is a key consideration if you are assembling docs from many parts.
Either of these two options might be a better match for your workflow and maintenance requirements.
- Keep the content in a single template and create new docs by making a duplicate and going to outline view and selecting chunks for REMOVAL. This appears to me to be a more logical workflow if you start at outline level 1, then expand to level 2, 3 etc.
- You could also create a macro to display the template headings in a Tree View where you can select elements for inclusion (which automatically selects all child elements) and unselect unwanted parts.