Is Jump Academy Training Maps free?

Yes. Jump Academy Training Maps is released under Community and costs nothing. Neither it nor Team Fortress 2 has any paid content.

What do I need to run Jump Academy Training Maps?

Team Fortress 2, which is itself free. Jump Academy Training Maps is an add-on and will not run standalone.

The PlayBound Launcher installs it in one click from Team Fortress 2's mods list. You can also install it by hand — full steps are on this page.

Roughly 120 MB, on top of the base Team Fortress 2 installation.

Yes. The source is published at github.com/TF2-JumpAcademy/JumpAcademy-Maps under Community.

Jump Academy Training Maps — Free Team Fortress 2 Mod · PlayBound