Is that the UTC-0500 one?

Trac has backlog and milestones (for epics and sagas) and plugins offer kanbans. It’s been OK when I’ve used it, including hosting one.

No, but could you feed the website with mismatched tags through something like tidy first? That error looks like maybe it’s expecting xhtml and getting html. Maybe the site is declaring one, then using the other. Lots of software won’t care because it’s a pretty common error, but some panics.

Those apt commands are in a less-good order. It’s usually better to update apt, then upgrade the system.

I upgrade as soon as reasonably possible after the notification appears, if the system isn’t on auto-upgrade.