Traditional "time-lime user" struggling in Unreal Engine

Hi Guys, I’m a "Traditional filmmaker, I use to work a lot in AfterEffects and I’m very comfortable working in those kind of softwares where the compositions happens in the timeline and it’s possible adjust anything in “No-real time”. Well, I’m trying so hard to jump into Unreal Engine to make some scenes and I’ve found some aspects that maybe are so simple but yet very difficult to understand to me. What I’m trying to do is to make kind of a “Cheap homestudio Virtual Production” With a green screen and this is the path that I planning to follow:

  1. Film my green screen footage with markers so I can track them using the camera solve from MochaPro in after effects and get a .FBX file.

  2. Create a camera in UE4 then paste the .FBX file so the camera moves the same as my footage.

  3. Mix somehow my green screen footage with this sequencer camera so the movement is the same

I’m very new with UE4 so here it goes some of the problems that I’ve found and maybe someone has any idea of how to solve them.

The first problem is that I haven’t been able to mix the sequencer camera that is animated from the .FBX file with my green footage, at this point I just have a compositiong with my green screen media and a GCI element of a camera in the background, and it actually moves when I play the sequencer, but I don’t know how to sincronice them both. Most of the documentation and tutorials talks about how to make virtual production in real time but as I don’t have the equipment or the stuff to do it I’d love to find a way to do it just with my pre-recorded footage. So, how can I preview that everything’s looking good? to make small changes and play again the sequencer little by tittle. Is it a way?

In order to this my last question is, what do these big productions that use virtual production get once they have finished a shoot. I mean, they get different files where they can separate actor from background, etc? or they just make a “Screen recorder” of an output and don’t have the possibility to retouch anything after finish and then they just paste the clips in a editor like premier. How does it works?

Thanks very much guys for your time and your kindly answers. I really appreciatte it!