6) The security model is two-fold
* At the instance level, 2 instances being "federated" means for every user on instance A, if any user on instance B is following them, that instance A user will be included in the public timeline on instance B (the "fire hose"). The same is true vice versa.

If A has "silenced" B, users on A can still follow, read, interact with users on B, but the B users will not be included in the public timeline on instance A automatically.

If B has defederated from A, no user on B can use that instance to follow, read, interact with any user on instance A in any way. You can think of this as blacklisting an email domain.

** At the toot level, you can mark a toot's privacy as being
public (fair game for the fire hose),
Unlisted (not advertised in the fire hose, but non followers can view them from boosts, direct links, or from your profile),
Followers only (non followers will not see them), and
Direct (basically DMs, but with an arbitrary number of users, as few as 1!)

4) Try to find a Mastodon instance that fits your vibe and whose code of conduct you agree with. Your home instance is kind of the people you would be interested to read even if you aren't following them. But there's nothing saying you can't switch or have alternate accounts.

5) screencap quoting and copy/paste quoting is generally considered passive aggressive or malicious. Use the boost (to get through^W^W^W) feature. If you don't want the original author to know what you have to say in response... Maybe don't say it? Use the reporting system to highlight abuse and bad actors.