Not sure why you put this in the "Adult Discussion" section because I don't think this qualifies. Maybe a mod will move it to one of the more appropriate sections.
Is 400gbs of JAV too much? I guess it depends on who you ask. For me? yes it would be. I mean how many times could I watch the same thing? when it comes to porn after I watch it I delete it unless it has a lot of rewatch value. Then I keep it around for maybe a week or a month and
then delete it. This has nothing to do with whether or not it is too much for you. You are the only person who can answer that.
Will you get in trouble for downloading JAV off filehosting sites? probably not. I wouldn't download anything real risky from those sites because that might get a knock on the door from unfriendly people. Most copyright trolls go after the uploaders if they upload a lot of copyrighted material to those sites and not the downloaders. Filehosters are supposed to ban uploaders that get a lot of DMCA requests though, so that doesn't happen often (the filehosting sites need to protect their own liability concerns). It also matters as where the filehosters server is located and local laws concerning such. As far as torrents go, the most active copyright trolls deal in western porn or movies and yes it is possible they might hit you up for a settlement.
If you are worried you might want to make room in your budget for a VPN. Here is a link for a decent review on VPNs' and a lot more on filesharing news:
https://torrentfreak.com/