Thanks a lot for the feedback! New SPs can be found at any point once you're past the tutorial, though you might need a bit of luck to find ships where scientists spawn.
About the variety, this is unfortunately the issue with game jams. The game is set up to have much more content than this (the original plan was six characters to target and was cut down to four, and the number of random NPC dialogs and skins got cut down to just two) ; but that's certainly something I'm taking into account for a later update if I make it happen!