@Dillius 

I think you got most of it :-)
but after you have deleted ER605 and before you adopt ER8411, add ER8411 and follow the wizard to get all the settings on ports etc., then you will not lose any settings such as ddns, vpn or other things connected to an interface.

try making a copy of your site with the copy site function and practice it before you start, and remember to backup the controller before you start :-)

  @shberge by wizard do you mean the standalone setup wizard for the ER8411, or is there another wizard in the omada controller?

  @Dillius 

Choose ER8411 here and follow the wizard :-) I recommend taking a copy of your site and practicing there before changing your router

Wireded network and Internett

  @shberge Interesting, I don't have such an option on my OC200:

  @Dillius 

yes you have when you delete your old router, but if you do as I recommended, make a copy of your site, there is a copy site option in your site configuration, then you can work offline without destroying anything when you test change router.