When I make a change on my JSON file, and I upload that to my server, do I have to go into my Developer Roku page and click "Refresh Now" under "feed status"? Or will it automatically update the content after some time?
If the channel isn't published yet, then yes, "Refresh Now."
If your channel is published, in my case at least, it automatically refreshes 3 times a day; you can see the times that they have been refreshed. I don't have any manual control to refresh my published channel.
So, I created a mirror channel that I do not publish, where I test my JSON file (with a different name). I "refresh now" and if all goes well, I upload my JSON file for my published channel.