I use this account for normal user things, but I want to auto-post social media content in a community I'm in (!taylorswift@geddit.social) which I own. (The content will probably just post 0-3 times a day).
Should my account be marked as a bot? Should I use a different account?
If you are going to use this account to auto-post, yes you should be tagged as a bot, alternatively I would recommend making a second account for this task.
If your account is doing something automated, then it is functioning as a bot, doesn't matter if you also use the same account for non-bot things. I'd just make a second bot account to avoid confusion and bans.
Keep this one for your normal comments/posts, and create a second one to use as a bot account to do the auto-posts, properly marking that account as a bot.