Coin

Yes. Coin is free to play on Steam, so there is nothing to buy to start playing.

The minimum requirements for Coin are: Windows 7, 64 MB RAM, 50 MB storage. It runs on Windows only. The recommended specs are in the System requirements section.

No. Coin is a single-player game.

Mostly, yes. Valve rates Coin as Playable on the Steam Deck: it runs, but may need some manual setup.

Yes. Coin is the full base game. You need nothing else to play it.