Hey! A lil advice - Do not think of this jam as lasting 10 days think its 5 and scope the game accordingly, cause you probably will need more time than you think. Also i've seen that you want free sounds so here's a couple suggestions: zapsplat for sfx and opengameart for music (you can find a lot of good assets not only music for absolutely free there)
Viewing post in First ever game jam as a complete noob any tips?
If you are doing pixel art then here's a great video. To sum it up the easiest way to choose a resolution is to take a base of 320x180 and scale it up as you see fit (so if you go 2x its 640x360). I would suggest going 640x360 if you are new to pixel art because doing 320x180 might overwhelm you a bit with trying to make every pixel count. If you are doing non pixel art, then probably 1280x720 is a good spot. Also you should look up pixel art rendering settings (it's pretty easy to setup in godot) or it might look blurry