Ivy is 100% free. We do review each podcast submission, but you should expect to see your podcast live on Ivy within a day or so. Ivy strongly believes in free speech, and so assuming your content is your own this process is basically a rubber stamp and more of a technical process than an editorial review.
Ivy automatically adds tags to your podcast. Once your podcast is live you can add, edit, or remove a tag from any episode, but we use all of the meta data in the feed to select tags including the description, keywords, and person rss elements.
Tags work both ways, so if we link from your episode to a tag, that tag will also link back to your podcast. In the very short term you may notice your episodes appear on your podcast page before they appear on tag pages, but this lag should be no more than a few hours in a worst case.
You can definitely add someone else's podcast. If you don't know what the rss feed is, you can submit a url to another service or even if you just give us the name we'll try to find it for you.