I spent a couple years in product marketing (as a change-of-pace from dev), and I handle "marketing" for my company. Here's what I have to say: you need to be very careful.
You say you're running lean and taking a minimal product to market. Great! What are you hoping to do with a marketer?
In product companies, the "marketing" department does a bunch of different things, usually with different people specializing in each:
* Product marketing management (PM): Pricing. Figuring out what customers want you to build. Getting customers on the phone. Understanding competitors. Building a position for your product that differentiates you in terms of features and benefits.
* Marketing communications management (marcom): Advertising and conferences. SEO. Deciding to have a blog. Presumably (I'm wouldn't know) marcom people are also botching Adwords at startups all around the world as we speak.
* Public Relations (PR): Getting you mentioned in the press, on blogs, and in analyst reports.
Which of these functions you needs depends on what market you're selling to. I have basically no experience selling to people like my mom, but decent experience selling to other businesses. Let me break that market down for you:
* PM: The whole lean startup minimum viable process is designed to do the PM's job, meaning, if you're following the Reis/Blank playbook, you're already doing this person's job. Also, in a small software startup, this is a core role. If it's not being done by the engineers, it should be the "CEO" doing it.
* Marcom: If you can write posts on Hacker News you can set up a blog yourself. You can't afford a marcom person who knows how to use Adwords well, and if Adwords is your strategy, I'll let Patrick chime in to make a case for you automating and engineering that process instead of delegating it to someone with an MBA. You should avoid conferences altogether until you have customers.
* PR: At this stage of the game, you can do a lot of this work yourself. Mostly it involves hustling with bloggers in your space getting them free copies and bugging them to write about you, and then rolling that coverage up to the trade press in your field. (Be especially careful of an older bit of Graham advice about PR firms --- I'd be surprised if he still stood by it --- they are galactically expensive and, to put it generously, will pay off either spectacularly or not at all).
It's possible that you don't want any of these functions, and instead you just want a "business person", by which you might mean:
* Sales: someone to call prospective customers on the phone and get deals to happen
* Channel sales/marketing: someone to call prospective partners/resellers on the phone and get deals to happen.
* Bizdev: someone to call prospective acquirers on the phone and get deals to happen.
None of these are really "marketing" tasks, and in fact these roles are traditionally antagonists of marketing (sales and marketing have a long and sordid history of blaming each other when numbers don't get met). And none of them are things you want to hire before you have customers.
A running theme here is to follow Jason Freid's advice: don't hire people until you are getting run ragged doing their role for yourself. At least that way you know what you're getting into and what you're looking for.