This is great for RPG games; I made up a small cut-down RPG ruleset for my 6yo, and was going to try to 3d print some figurines, but...

This way, I can get my kid to make his own monsters; while he can't run blender to produce his own monsters, using these paper templates is sufficient for him.

Those look delightful! Eg for the next RPG session. On Google, the search term "papercraft" yields a lot of other results with easy to assemble models

Does anyone have any glue recommendations for these types of project?

Any idea of scale? Could I use them as scenery when DMing?

What kind of paper should be used for these folding projects?