Every account gets one Free server. Paid plans get more CPU and RAM, run 24/7 and can use your own domain. Add as many servers as you like to your basket.
Your server can briefly use extra CPU for things like world generation. If it stays busy for more than a minute it drops back to its base speed until things calm down.
They restart every few hours and go to sleep when nobody has been online for a while. Press Start in the panel to wake them up.
The server stops, but your world and files are kept for a while so you can renew or download them.
Yes. Open its panel and press Upgrade / renew. Your world and files stay exactly as they are.