We’ve used a couple of different Pis and a couple of different Odroids. The Odroids have been excellent and trouble free, the Pis not so much. Initially we got a Pi because we thought with the bigger community and better software support it would be easier to troubleshoot issues. Except that they have been regular problems that we haven’t always been able to work around or fix. One of them got relegated to a retro game ‘console’ because it was more trouble than it was worth. We’ve had little issues with the Odroids that wasn’t easily sorted.
Obsidian can be almost anything you want it to be. Try searching out some videos from folks who use Obsidian for journalling.