FWIW you can also use an account on i.e. Mastodon to follow twitter users. I suddenly realized because I was following a twitter users through a gateway, probably because someone had boosted a tweet from that account sometime and I had followed based on that.
That should take care of following at least.
Publish (on your) Own Site, Syndicate Elsewhere [ https://indieweb.org/POSSE ]
Publish Elsewhere, Syndicate (to your) Own Site [ https://indieweb.org/PESOS ]
Not everyone has eating the world as a goal. Lance Ulanoff didn't understand this when he declared Mastodon DOA two years ago because he couldn't find William Shatner, and people continue to make the same mistake. I don't want to follow William Shatner or Lance Ulanoff, so they can stay on Twitter with people who do.
If your goal is to have Mastodon "catch on" and have people transition away from Twitter en masse, then yes, you need William Shatner on Mastodon.
Even the main Mastodon project instance is funded by a Patreon. I don't think Eugen would complain if he had a few more users, but growth doesn't seem to be the #1 goal. Only the tech press and its target audience seems to care about how fast Mastodon grows. They are free to start a growth-focused instance.
The instance I'm on has 800+ active users. The numbers on closely related instances are probably similar. That's plenty.
You can't get your Startup Founder porn from here or one of the other umpteen social sites? 60% of all social media seems to be from "successful founders" or "influencers". Hard to imagine anyone finds a dearth of that stuff.
If you do join choose your instance wisely, beware that many instances block mastodon.social, freespeechextremist.com and similar for being hot messes that have no moderation. The latter instance in particular has a very persistent hellthread spambot problem, where bots sling nudes without content warnings at people constantly.