I suppose the vast majority of users will use the forum without customizing anything.
For this reason, I suppose I should carefully choose which categories will be displayed by default on the sidebar.
As for your customization suggestions… They’re good. I was never using new topics and unread buttons in the navigation, but now they are available in the sidebar, along the categories I selected, I use them daily.
It (and I) changed my habits, and my experience is improved.
The only thing that bothers me regarding tags is that some are very underused on meta.
A single example: Topics tagged css
7 CSS tags in the entire meta forum? CSS topics have my attention because I’m skilled enough to help people trying to customize their Discourse, but since the tag is never used, watching it seems useless.
By the way, here is how my sidebar looks like now 
