My delta comparing to upstream is 2 985 files and +287k only since Oct 15. That's crazy, and upstream is moving fast with more than 500 commits... Do you guys have any advices on how I could handle that better?

I would suggest stopping adding new things now and instead try to push what you have upstream. Or else you will just continue to drift further away

Indeed, but I mean that's just 2 weeks of work, so should I actually merge on a daily basis or something?

one or two features at a time, complete them, then move on....that is my strategy anyway. If you wait to long before you push your changes, someone else pushes the same feature and your work is a waste...

Thanks for the advice, let see...