1st Marketing Person - how to hire?

By the end of January, I want our MVP in front of customers - we think it'll be a mass-market self-boarding B2B SaaS situation (fingers crossed). I have no great concerns on the engineering front, but I worry a lot about the marketing: I need someone figuring out how to get visitors onto our websites, presumably through some mix of interviews, content marketing and advertising spend.

However, we are currently a tiny "all engineer" firm; we have never hired for anything that didn't involve lots and lots of coding before.

• What should we be putting in that job ad?
• What does skills assessment look like for a role like this?
• Has anyone tried project-based hiring for a role like this? (Fixed spec, fixed price, "get to know each other better")?