Absolutely, however you are not picking the best tools IMO. I would look at GitLab, which has stronger project management and issue tracking integration (as well as a free self-hosted version). Another solution is to evaluate Phabricator as it has a stronger feature-set in some areas.
GitLab Omnibus has Mattermost integration, but you could also look at Rocket.Chat (and in all honesty Discord is a kickass free alternative to Slack).