There are search operators listed at https://fedi.tips/how-do-i-search-for-stuff-on-mastodon which work on the website interface and the apps too.
You can optionally make your public posts searchable by their entire text content (not just hashtags) if you opt into full text search: https://fedi.tips/how-do-i-opt-into-or-out-of-full-text-search-on-mastodon/
Terminated my accounts at Meta's Instagram and Threads...
Now working on helping my community set up a possible alternative to our very useful Facebook group. Leaning toward WordPress/BuddyPress but open to (serious) suggestions.
UPDATE: There's a good conversation in the comments below. Thank you to all who are offering suggestions.
@grayautumnday Hi Autumn. If you haven't found this yet, https://fedi.tips has long been a valued guide for those of us bumbling about in the misty fediverse. For your specific quest you might scroll down to "The Fediverse Beyond Mastodon."
Worth noting too is that, as at Hogwarts, help will always be given to those who seek it! Truly: use the hashtag [#]help or tag your query with [@]feditips
Cheers
There are lots of guides for beginners at https://fedi.tips that cover most of your questions.
You don't need to crosspost because all those platforms are on the same social network. Poeple on Mastodon can follow accounts from Pixelfed etc, they don't need to see the posts repeated elsewhere.
You probably don't need to join multiple instances:
https://fedi.tips/do-i-need-multiple-accounts-do-i-need-to-join-lots-of-servers
A guide to instance types:
https://fedi.tips/what-other-kinds-of-servers-are-on-the-fediverse/
If you have any other questions feel free to ask!