Jeff,
I would recommend ignoring SEO for awhile. You have a long road ahead in outpacing your competition (assuming you're in even a mildly competitive market), and a lot of normal marketing practices are going to move the SEO needle for you (slightly). And, you don't really yet know what search terms are going to convert for you, so you'll want to first do some planning before you build your whole website around search queries you've only guessed are valuable.
As for content, when you hire cheap writers, you run into a lot of duplicate, or 'spun' content. For an explanation on the Google algorithm update that tackled duplicate and low-quality content you can read about it here: http://searchengineland.com/library/google/google-...
If you're unsure if your content is copied, just copy a sentence of the article, and past it into Google search with quotes around it. If the same article shows up on multiple websites, it's worthless (unless other sites copied your content, which Google, even still, has problems with attributing the original author, unfortunately). Before you approve content on Fiverr or Upwork, be sure to test it out to make sure it's original, before you approve and purchase.
When evaluating search terms, the volume of searches is not the only consideration. Before venturing into SEO, I recommend my clients start with paid search via AdWords. Before you spend 9 months, and hundreds of hours building your website to rank for a target term. Wouldn't you want to spend $50-$100 making sure that term converts for you? Target that exact-match term in AdWords (not broad match, explanation of match types: https://support.google.com/adwords/answer/2497836?...) and see if your website is converting those terms. If you're not converting those terms properly, then there is either a problem with your website that needs to be addressed, or the actual intent (not your perceived intent) of those terms, don't match what you're offering. Just like doing your research on a house before buying it, you don't want to buy the house THEN do the research after the fact.
Also, be skeptical of other's SEO success you read online. Just because an SEO tactic worked for one person, doesn't mean it will necessarily work for you in your market (or SERP: search engine results page). My wife makes a very clear point about this, by ranking an article #1 on Google for 'monkey balls in Louisville Kentucky' - because there's no competition for that term, she ranks #1, and it took zero SEO work on her part, other than writing and publishing the article. Obviously, she's received zero traffic for this term. So, the next time you hear an SEO company say "We rank #1 for 'Houston's best SEO company on earth' you need to remember that if nobody else is trying to rank for that terms, it's an easy term to rank for, and their credibility should not be assumed by them having a #1 ranking, but by how competitive what they rank for is. My agency ranks #2 for 'ppc management' on Google. It brings us quite a bit of business. If it didn't, it would be a worthless term to go after - and we knew it was worth going after because we tested it first.
To answer your question on the cost of SEO. A few hundred dollars a month is going to be hit and miss. We've provided SEO services for multiple fortune 500 clients, and the amount of work it takes to rank larger brands is easier in many cases than ranking smaller sites. Many great SEOs aren't going to take small jobs, and those that do take small jobs must not know their value, or they would be taking the bigger jobs. So, in that price range, you're going to run into more practitioners who are guessing, or using your site to practice SEO, rather than implementing from experience. You are their experience. This doesn't go for all, but it goes for most in that price range. We don't do anything for less than 5k/month, and even then, we are very picky, because it's a lot of work, and it requires a client that follows our instructions, and doesn't go rogue and do things that harm the site's SEO without consulting us (buying links, etc). So my advice for separating out the good SEOs from the bad, are to hold them accountable, make sure your reports are showing the same metrics each month (not just the metrics that are positive for that month). Speak to references, and make sure you have analytics properly set up, so you're properly evaluating their performance. Keep in mind that because Google doesn't provide much keywords data anymore, an increase in your brand searches can easily be mistaken for an increase in SEO. If thy are showing you a report that SEO traffic went up 30% from last month - did you run a tv ad that increased brand mentions? Be really careful with that, because it's not always clear if what they are doing is actually working for you. And, if that increase in non-branded traffic isn't delivering results, then the added traffic is essentially worthless to you.
I hope I addressed all of your questions. My recommendation is to put $50-$100 a month into AdWords, for a few months, and start testing out terms that you think your target marketing is searching (start with some common sense terms, and work from there). Be sure to have conversion tracking set up, so that when that conversion happens, you can identify which keyword brought the lead in. Call tracking (We use calltrackingmetrics.com) can provide call tracking that also tracks back to the keyword, so even if they call you, you'll still have the keyword. Keep the keywords that work, remove the keywords that don't, until you find yourself with a cost-per-conversion that is profitable. Then, once you've identified a handful of keywords that convert for you, go ahead with SEO, but stay on top of your provider that they stick with the plan for ranking on those keywords, not just the keywords they find easy to rank for (with unknown value).
Also - remarketing is a no-brainer in my opinion. If someone comes to your site, you want them to see you everywhere for the next couple weeks. You can do remarketing through Google's display network, as well as Facebook. Both are very effective, and pretty easy to set up.
I do AdWords for a living (my wife and business partner does SEO), so I can talk about it all day. If you have any other questions, I'm happy to share what I know.