Huh, I'd also like to know this!! If anyone figures it out, PLEASE!

While I'd obviously recommend choosing a European hosted instance, it doesn't really matter in my opinion, as long as it's well interconnected with other instances. Look for and subscribe to hashtags relevant the topics that interest you, that way you'll find interesting accounts from all over the fediverse.

EDIT: Also make sure you use relevant hashtags when posting so you can be found too!

I am happy with social.tchncs.de Edit: The only relevent part: it is well moderated. The rest i solved by following hastags and people

That's a tough one. If you need wide reach but also want something better moderated than e.g. mastodon.social I don't have any other suggestions than journa.host, but they've closed account registrations right now.

You might be able to contact and ask them though, if you present your idea for an account in a good manner they might make an exception: https://journa.host/about

Edit: not sure where the server is hosted, though. The admins seem to be mostly from US so not sure if my suggestion is a fitting one for this community. I'll leave it up anyway incase someone else knows and can fill us in.