How can I get macOS to notify me only once per minute/hour/interval vs for every single event?

You can change those things in Settings for Notifications both on the iPhone and on the Mac.

For the iPhone, you can disable the second notification for Messages in the settings. You can also disable the sound (or change it) for messages, emails, phone calls, basically everything. On the iPhone this is done in Settings => Notifications and you can adjust the notifications for every app. It sounds like maybe you want to keep the banners but eliminate most of the sounds? There are various options for this, lots of flexibility in the iPhone Settings. Similarly on the Mac, in System Preferences choose Notifications and you will see similar options. You can even turn off the sounds for everything if you want. You may want to leave on the sound part of the notifications for some applications, however.

For the banner part of the notification, you can make the banner persistent (it stays on the screen) or have it just show for a short time. You can also choose whether they show on the lock screen or not.