Help with some tips pls

Help with some tips pls - student project

Hey guys! For now i'm just reading stories for kids on my entertainment Youtube channel. What i want to ask, like starting tips. I film with my cellphone which is a OnePlus 6, it films on 1080p or 4k, but when i move my videos on my laptop and then upload them to Youtube i get a shitty 320p maximum of video quality.

I also have a canon eos 200D as a camera, but never used it for videos. Can someone recommend me something reasonable to start filming for Youtube? 

Second thing, in what can i create ok-good thumbnails and a cute intro for my videos? Thank you. My channel is Zouka Events, if you can/wanna check it out.