Would it be possible to either set the anchor note icon to default to last use (e.g. key instead of notepad) so that everything I create an anchor note I don't have to change it? OR set anchor note prefs in prefs.
You can set it in a hidden preference. See the Wiki for details. Last used icon is not consistent, therefore wrong. And I find it too small an issue to warrant even more UI in the already pretty filled Note preferences.
You can also set this hidden preference using AppleScript, there's a sample script for this on the Wiki.