There are a lot of issues on Steemit. Some of the problems are not so easy to fix. If the bots didn't practice selling votes openly as they do, then it would be done in secret, hush hush like, and then it would be even more difficult to identify abuse.
As far as you giving downvotes, on Steemit, I go with "when in doubt, don't". Do some research on what the downvotes are for, and what they do. It should be covered in the FAQ.
Advertisement on Steemit will never happen. That is one of the points of this platform in the first place.
Self voting is an issue, but if it wasn't allowed, then people would just make multiple accounts, post with one account, then upvote it with a different account (people are doing this anyway). There are a lot of loopholes. There are people working on these issues, though I don't know the extent. But these problems are why the platform is in "Beta". It isn't perfect, but it is a Beautiful place. Behavior like that of grumpycat and his alternate accounts greed diminishes that beauty in ways that I just can't put into words..