Yes! The pack is licensed under Creative Commons (CC0). You can use the models for either personal or commercial projects without giving credit, however its very appreciated.
Ofcourse! Most of the models inside the pack have a low number of polycount/vertices, which will result in much better performance in games compared to using high poly models.
If you're making a film or animation, a low number of polygons/vertices will speed up your viewport and rendering times.
Nope. All of the models have all of their textures included and packed inside blender, so you can put your .blend files anywhere you want them to be without the fear of textures getting lost and having to re-import them.
On the other hand, you can also export a copy of the textures from the models within Blender.