It's definitely not designed to develop a microsite, but that doesn't mean it's not possible. For example, you could build a landing page template with the header/footer you want to be common across the 'microsite,' as well as the navigation that would have a link to each of the individual pages on the microsite. Then you'd build the individual pages, and update those links in the placeholder nav to point to each of those landing pages. Basically, you're just making a network of landing pages that interlink to one another.
Is there something prohibiting you from using a proper CMS rollout? I feel like anything more than just a few pages would be a nightmare to maintain if you built it using Marketo.
This is usually something you'd build using a content management system, like Wordpress, Drupal, etc, and then you could use Marketo forms and the Munchkin javascript code to track users and collect leads on your microsite. Content management systems are generally a lot more flexible and designed to build web pages and microsites.
Marketo was designed to build standalone landing pages to support specific marketing campaigns as opposed to multi-page web experiences. What's the purpose of the microsite, lead generation?