>>718648592
There are side missions that can be done out of order, but the weird thing is you don't get side missions until you're sheriff. (You depose Benny.)

See the legend on the map. It shows the icon for side missions. There's actually a quote from the dev diaries about this:
>Taking place after pivotal moments in the main questline, these adventures will offer you the chance to explore Seattle at your own pace. You will be visiting its Clan leaders, keeping the competition at bay and making decisions that will affect the outcome of your journey as Phyre. These are stuffed with Narrative and lore and I'll be taking you from the depths of the underground to the snow-capped high-rise rooftops.
I think Paradox would be wise to focus on the post-Sheriff gameplay for their official stream (I think it's next week?)