Hey man!
Wow…looks so so good 
When I first saw the thumbnails I was like…wait, thats a photo or v-ray render xD Very nice quality push 
Just some minor questions^^… You said earlier: “I use a intensity of 6 for the sun and 16 for the spots, depends of your auto exposure. For exemple I used 1.0 for Min and Brightness (so no auto exposure) and 0.5 for exposure bias.”
16 for the spots? So you are NOT using inverse square falloff?^^ I always have a hard time translating the values just by looking at it 
Also…with exposure settings like , dont you have to almost kill the bloom completely as well? Locking high to 1 AND adding the 0.5 offset triggers quite some bloom if you are not tweaking that one down a lot as well
Another thing I would find interesting…how do you setup your reflection capture actors? First, sphere or boxes? I mostly use boxes for rooms and spheres for details, but the boxes have quite a lot issues with rooms that are not rectangular (like T shapes etc…you get quite some noticable blending issues). I am also asking because of the stairs^^ Is it just one big box actor covering the hallway and the stairs? That would cause some heavy offset, but my guess is you just dont see it because conrete or wood is not a perfect mirror^^
Yeah…just some thoughts^^ Looking forward to see more breakdowns and nice videos
Cheers!
PS: Wait whuuuut?!?!? You can calculate Lightmass in under 10 min with these crazy ini boosts AND bounces set to 100 (while 3 is the start value^^) in the world settings? Sounds like magic