JAC Ok. My only other guidance would be to adjust your GA (Google Analytics) if necessary so the correct domain is reflected. I noticed you are using the SEO extension in Flarum, so you might want to postpone your decision to delete the other domains for a month, and tell Google you're transferring domains. Otherwise, the existing entries in google will show a 404, and won't look good - particularly as there will be duplicate content under a different domain
Have a look at this
You'll see what I mean. There are an abundance of links crawled by Google, and it makes sense to have them redirected.