Final 8 will be just like the Final 6 in past, but I don't know if they will carry over points (7 to 0) like before. It will be single round robin so 7 matches, regardless of conference.
Best team of Final 8 goes to Final, while 2nd and 3rd place teams go to Final 3 semifinal, 2 match series, if team wins both matches they will advance. IF tied at 1 match each, then 25 point Golden Set.
Final is similar to Final 3.
As for Promotion/Relegation, the V-League will be at 12 teams next year, 6 in each conference. If the V2 winner has a S1 license for V1, then they will be automatically promoted. Right now Victorina Himeji is 5-0 in V2, but as a new team they have a S3 license. Whether that can be upgraded to an S1 in 1 year is not known at this time. I would guess that they cannot do that, so they may be stuck in V2 for one more year.
Only JA Gifu Rioreina (3rd place 4-1) and Breath Hamamatsu (7th 2-3) are the only V2 teams with an S1 license at this time. That could change over the rest of the year going into next year. All other V2 teams are S2 licenses (cannot be promoted to V1), excluding Victorina.