For the second one, nothing stop you from publishing a demo/prototype for this game jam like all the participants.
And if you enjoy your project, spend more time to add content and polish it for a paid release in the future.
For the first one, I'm not sure but I'd say if we use game engines, you can definitely use some pre-made assets.
But we have a month, so plenty time to replace every placeholder with cute handcrafted new assets just for the occasion X)
Just don't throw templates, plugins, assets from Unity/Unreal/any store/library and call it a game :3