As of this moment, it only runs on Windows. We are currently working on two solutions to bring it to the Mac: a native application, as well as making our Windows codebase work with the Mono Framework as a holdover until a native app can be written.
They won't necessarily. Kits are going to start being built as soon as the documentation and video tutorials on assembling the printers are complete. Until those are complete, everything is being assembled and shipped first-come, first-serve.
Don't see the answer to your question? Ask the project creator directly.