Are you going to provide the videos and the metadata information (title, description, tags , category) or is the uploader supposed to source videos and write up titles and descriptions ?
Whoever you chose will need to obtain 400 different videos, because sites like xvideos do checks against the submitted videos and will reject already submitted videos.
This is the reason why my (at the moment preliminary) price is so high, I have performed similar projects in the past and I'm aware of the complexity and time it would take to prepare so many videos and post so many videos in a single day to a handful of websites.
I would appreciate it if you can clarify these things and I would also be interested if you would be flexible, for example upload 20-25 videos per day but the same total number of 400 videos (over the course of let's say 7-10 days (40-60 videos per day)