There are a lot of variables here.

1. Using just chords - no problem, not copyrightable in the first place.
2. Melody is the identifier, this is the thing that can't be used legally without paying royalties or without permission from the copyright holder.

One question to consider is how much of it is YOUR music if you are using the defining characteristics of an existing piece of music?

There are certain laws in effect in different parts of the regarding arrangements of existing material, but an arrangement is (usually) a substantial and original alteration to the original, which is different to a cover in the sense that I think you're talking about it. However, a cover (and cover bands, for eg.) often do their own arrangements of material.

First, does this extend to remixes that include no samples from the original? Using the same chords, melodies, etc. My gut feeling is this would be considered a 'cover' but whether the cover/remix terms are interchangeable is debatable so I thought I'd ask anyway.

Second, should I create a track that uses non-licensed samples (for example, from a TV show or another song) can I upload a version without the samples to WB, and link to the full version on Soundcloud or Youtube? My assumption is that the reason these rules exist is because of the site's liability in hosting copyrighted material, so it seems reasonable to me for that to be the workaround.

Thanks for your time!