1. There’s a toggle under in the settings where you can silence unknown callers, meaning callers that aren’t in your contacts will be silenced automatically when they call you. (No vibrations etc, just a notification banner that tells you someone is calling and that banner disappears after a few seconds)

[Settings > Phone > Silence Unknown callers]

1. Similarly, there’s a toggle that will filter all unknown texts and put them into a messaging folder for you. There’s no way to mute or not receive them, so this might not be helpful for you.

[Settings > Messages > Filter Unknown senders]

1. I can’t really help with this, so hopefully someone will share a tip for OP.

2. This one is pretty easy. Go to the contact of the person you want to call, click on their name, under the notes section, you could put a letter “a” or “important”. The next time you wanna call, you can go to the [search] tab in your contacts and type “a”. That person’s name and number would appear and all you have to do is click and call. If you have multiple people you commonly call, you can put “a” in the notes section for all these people. It works too.