when I see that whichever instance I choose is defederated from another bunch of random instances, is it possible to have those show in my feed without making a separate profile from other instances? and can I turn them off again if I see that defederating was the right idea?
Yes, but It’s pretty hands off since 99% of security stuff is managed for you by the Lemmy software, including rate limiting. Just make sure you use a secure password and if you want put the instance behind cloudflare which is super easy to do.