I few recommendations Ill give you since you have slow connection. Some are a general rule of thumb

1.  Create controllers that has the basics for each genre of games you plan to make in the future.

for example I have a Game Controllers Project. that has an;

FPS controller - 2 C# scripts, 1 for player movement the other for a parented camera's rotation

Third Person Controller 2 C# script , 1 for player movement the other for  camera rotation

Platformer Controller- just one Character controller script

Also create basic mechanics needed such as a simple saving system and an inventory system.

(Disregard this if you already got this down)

You could occasionally build the project to see how big it is, then calculate how much time uploading would take. Then you can calculate when the latest is you can upload.

Other than that. Keep things as simple as possible!

Good luck

Happy jamming!

Same here, working at the lowest possible tools, internet. Plus I don't know what I am gonna do? Which platform builds will be needed? I don't know. Hope at least I can participate. (Literally internet is so unstable idk on the very crucial time it won't work) 

Do you think I could get it done?

Create a private itch.io page that you upload the latest build every day.When you are done with your game you can simply attach the page to the jam submission DONT forget to make you page public this way even if you donnot manage to upload your latest build in time the most recent build will up and running.

I wish you the best of lucks!