Hi!
I can only give you a veryyy rough time estimate as it so heavily depends on if you read fast or listen to all the audio in full, find all the hidden stories, beat the characters in the rhyhthm game etc. But if you're an excited player that will probably want to engage with those different parts of the game. I think runtime will be around 5-10+ hours.
This is my first own game project.
And indeed would love to create a second game which would continue Sam's story but take place a few weeks after the events of this game. Don't want to give anymore info, as Im early stages just thinking about that but all subject to change. But yes, plan is definitely to start work on a second game right after this one is released :)