Do they have to be files I uploaded or can they be files that other people have uploaded?

People post content they didn't rip all the time. Everything I have are stuff I have accumulated from the web over the years. Individual posters have varying attitudes to their rips being reposted. Certainly, you should respect their policy (if they've stated one.) Some are fine with just credit, others less so.
It is ill advised to repost something which is someone's rip immediately after they did so. This has started a lot of flame wars and is best avoided. I have done so only with the specific permission of the original poster. How long is long enough to repost is a tough question. I can't think of a hard and fast rule. (although I believe after the original link has expired is fine.)

I am aware that a lot of stuff only circulates because people are reposting others rips. Just be aware such actions can have consequences, aggravation being one of the least of them.

Posting links from other web sites are considered, at the least, a faux pas. Some people feel stronger about it then that. At the very least, reupload it and post the new link. Reposting an actual link has implications about increasing its presence in search engines. I can't say how true it is, but for this and other reasons, some posters take offense to such practices. (See above)
Posting links to web pages within this community (but not the link itself!) is not a problem, (at least I hope not, I just did that yesterday,) since these links have the original poster's creds in the post.

Needless to say, there are many other opinions on such matters.
JonC

Thanks for your help. I was considering posting a MediaFire directory of Bemani albums, but I may reconsider.

If you're willing to do the legwork, just download and repost. (After considering above)
JonC

There are no fast "rules", and opinions vary widely. All I can say, as far as linking to sites, is that I did it once for a site full of Doctor Who audio, and soon after, the threads had to be removed, due to protest from Big Finish. Did my linking to them here increase awareness and lead to the removal? I doubt it, as there was little in between time, but I don't know. And that possibility bothers me.

Another thing to remember, is that if the link is posted on a private blog, most frown terribly on direct linking. And, many post on private blogs, and not open forums like this, in order to somewhat minimalize where and how the rips are shared. In the end, it all comes down to personal choice. Repercussions can vary from angry comments, to getting banned from private sites. But as far as posting here, aside from the various label restrictions, there are not many actual "rules" you have to follow. Just...common courtesy, I guess. When in doubt, one could always try contacting the OP, and ask if it can be shared.