Governance: Guidelines and design standards

Great question, sorry I just now saw it.  Governance is a big topic, but in my experience it goes easier if you have the right mind-set about it to start with. Generally, governance should provide a framework of best practices, guidelines, and boundaries - with the goal of simplicity. Most successful organizations have different guidelines for different use cases.

• For sites based on communication / publishing uses where the content is open to all, they're typically more strict on things like look-and-feel, layouts, permission levels, and so forth. The idea is to prioritize a consistent experience for the users rather than ultimate creativity for the site owners.
• For sites based on ad-hoc collaboration / teamwork uses, the rules are typically looser on those issues. Let the site owner and team figure out what works for them. It's a private space anyway, generally let them use what works for them.

It sounds like your use case is more like the first bullet, so a little more control and consistency is probably appropriate. The key thing to keep in mind is that every governance decision you make will affect your adoption rates - for the good or the bad.  If you try to lock down or control many of the out of the box features, you will frustrate your site owners and power users. If you don't offer any kind of framework, those same site owners and power users may create a mess that isn't very useful to the audience.

Another key concept is that it's common for governance to evolve over time. In fact, it's dangerous to assume you got it exactly right at the beginning. If you start looser, you will at some point probably discover areas where you need to provide some stronger guidelines. If you start tight by forbidding anything other than basic functionality, then you really must be pro-active about expanding as your users comfort-level and skills grow. Otherwise, you create an artificial ceiling that kills adoption rates.