New to this whole concept need a helping hand

[MessItUp]

Hello to all of you out there,

I am fairly new and also fairly lost. I owned (and still do) a Sony A-55 which is slowly failing on me, and I do more and more video, however with a average of 17Mbit bitrate output it is fairly poor quality. So I was hoping to upgrade. First I was looking at the a6400 from sony or a fuji x-t30. Somewhere along the line I fell into a tunnel, I was looking at older fullframe a7s camera's and then I found the interesting high bit (12/14bits) and raw 4k recordings at Youtube with magic lantern on a 5D2. Now the 5D2 has always been my dream camera back in the day. Back on topic... I don't mind a bit of fiddling, tweaking and so the idea of getting a old fullframe 5D2 camera and maybe some vintage lenses for video shooting has become a serious thought.

However I have never been into canon, magic lantern, never to much into vintage lenses a little into cinetography.
So... what to expect, what is really possible with a 5D2 to capture 4k, how is the quality really? Will it be able to outperform the newer camera's I metioned? Perhaps with some hard work (lifting more weighty gear, manual focussing, postprocessing more). Does it do 4k or was all I have seen upsampled? Is there enought information do good upsampling?

Also can you point me into the direction of what to expect with vintage MF lenses like a decent budget kit of say a set of high speed (<f1. 20-24mm , 35mm , 50mm and perhaps a 85mm primes.
I know, a lot of questions, but maybe you could convert me for life.