Welcome to the site. My foremost advice for starting out is to, well, start. Nothing kills more projects than getting so lost in hypothetical ideas and features that you lose sight of actually making it. Pick an engine and go. If you’re completely lost with whatever engine you choose, follow through online tutorials until you get a good grasp of its workflow and mechanics.
If by “in game jam fashion” you mean under a tight deadline, that’s also a good idea. It gives a hard limit to your scope, helping to prevent the issue of feature creep. If you go through with this idea, remember that your deadline is self-imposed, and there’s no shame in extending it by a couple days to get what you have wrapped up and published. I did exactly this for my own game The Gloucester Estate Spooktacular, and it turned out my best product yet.