I have to chime in and say this feels a bit underthought feature. I use a throwaway email for everything possible, and I would imagine a large portion of Fediverse users do that too.
I also get the motivation behind the feature. I didn't feel like throwaway addresses are worth it before I started using them. They may seem like an obvious spammer flag. But I'd say it's 50/50, just like with any free email provider like gmail or Proton mail.
I haven't tried an OG Mastodon server, but currently running a GotoSocial instance, just for me.
With mostly the default retention etc. settings, the instance takes at most a couple gigs of storage space. If some image has been rotated, it will be refetched if you view the post again.
As for Federation, a single user instance is probably not a good idea if you're just starting with the Fediverse. Only content from accounts a user on your server follows will reach your server, including posts boosted by the people someone follows. I was already following about 150 accounts when I set it up, so I didn't really notice much difference in the home feed.
OG Mastodon can utilize relays, which will help with the lack of content.
For following topics, I made another user that follows some hashtag bots from fedi.buzz. The bots boost all posts with specific hashtags, so the posts reach my server.
If I were to do this again, I'd probably go with full Mastodon instead of GtS, just because I like the UI. There are other niceties too.
I think there's no way to keep the same domain while changing the underlying server software, without breaking federation. If someone knows a way I'd be really interested.
True, I failed to mention that I think there could be a setting to enable the feature, or dismiss the warning per-account. @rimu@piefed.social maybe consider this?