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Welcome to one of the greatest hobbies ever!

• Many TTRPGs can be played with any number of players! Typically there is a GM & several Players who make up a party of PCs (Player characters). I've played with as little as one other player, but typically 3-4 players is the sweet spot. Of course it varies from group to group. Try it out with 3 of your friends and see how it goes!
• Most roleplaying games (this one included) have varying play times. You might run a one-shot that only lasts 2-4 hours and have tons of fun. You could also play a "campaign" which takes place over multiple play sessions but continues the story with the same characters, much like a seasonal TV show. Campaigns can seem extremely daunting to run at first, but really you only need to drop the players into some classic action to get the ball rolling. 
• Lots of YouTubers & bloggers have covered solo roleplaying. These games are typically "best" enjoyed with a group of trusting friends but you can certainly find some enjoyment in solo play. There are systems called "Oracles" which allow you as the player to ask questions and receive answers about anything you might encounter. 

Hopefully these answers help. TTRPGs are a wonderful act of shared imagination and storytelling, one of the most enriching experiences you can have as a creative. Have fun!