Adwords would be another possible option for you.

You could always literally just promote the article, but I don't see that as the best thing to do. Usually the idea with content marketing is that you benefit from the host website's popularity without really needing to do anything. But if you find that you have used a solid keyword in your article and the article is even slightly ranking in Google... One thing you could do would be to build some backlinks to the article to boost it. Even just a cheap press release and a few high PR links would probably do it. But that's a bit of an advanced option.

I wouldn't be too discouraged yet. You really haven't even cracked the surface of this thing yet. Your offer is converting and that shows that you have the basic components in place. What you need is cheaper leads. I would start at the beginning and set up a more straight forward FB ads campaign as described before. Then it comes down to looking at the price of your clicks and the conversion rate of your site. If the clicks are too expensive then you need to keep tweaking your ad. If the clicks are reasonable but your conversion rate is below 20% then you need to keep tweaking your squeeze page. Looking for new sources of traffic is not the path you need to take right now. Getting the entry to your funnel optimized is, at least in my opinion. I have no doubt you can make this work with FB given the early signs. But if you are getting leads for less than $2 each and still not making a profit, you'll then need to look at the funnel copy and process.

I would. I think Yahoo and Bing are good for people who want to start small with PPC or add a bump to their existing PPC. But for you they might be a bit to small and a-typical for you to gauge results properly until you have other results to compare with. I would really play with FB a lot more first until you can get that price down. All PPC takes some fiddling. Adwords would be another decent place to start. Though they will make you jump through some hoops with your landing page.

I do get reports semi-often. Meaning if I blast my list, inevitably one or two, out of thousands, will say they can't watch it. But I can never duplicate it on any machine. As long as you browser test with the major browsers my guess is fine. Out of any decent sample size you are going to have some old and out dated machines, and problematic connections.