It doesn't matter if you vote first on a post, if whale votes later, the post will still earn a lot. If more users with a lot of Steem power vote, the reward will start increasing significantly. Your $12 post was probably upvoted by Curie guild that helps in discovering fresh authors and their undervalued posts. You can vote more, probably 40+ votes per day with 100% power and you'll be fine. :) Comments are like posts so all rules apply there. And, of course, there's nothing wrong with voting on your own posts, almost everyone does it. :)