Plugin a custom renderer

Hi,
I`d like to use ue4 as an educational tool for rendering techniques, to try out raytracing, forward and deferred approaches, not going to use ue4 material system, hardcoded shaders are better for my usecase, so my questions are:

  1. Looks like ue4 has a separate logical and “send to hardware” scene representations, if that is the case where the translation takes place and does it happen in-editor when it builds the game, or the game has this logical scene as well?
  2. Ill need to have a gl or dx context anyway, can even get it from rhi i guess, so id like to draw Slate ui to offscreen buffer and then composite it with rendered scene - is that possible?
  3. How to link to animation system, current pose would be enough for the starters
  4. Is it possible to have custom content processors as we import assets from fbx or create texture images?