Picture the scene:

Deco M5 arrives. In order to avoid the wife and family rioting in the hallways over lack of internet access and me losing work time (working from home) I quickly disable the existing wifi devices and set up the Deco M5 in AP (access point) mode with the same main and guest wifi SSIDs and passwords that existed before. This way I don't cause disruption to existing wired network devices (NAS, VOIP telephone hub, home automation device hub) occupying static IP addresses assigned by the existing router DHCP service. And most devices in the house reconnect to wifi as normal.

In under 30 minutes I have an amazing wifi service around the whole house that allows me to also remove the old ethernet oer power circuit wired network. The only casualty is the old Nintendo Wii that cannot connect to wireless n or ac (oh well) and a laptop that had to have a wifi driver update forced on it to successfully connect.

I really want to use the M5 in router mode, but I also want to plan exactly how I will configure it before I start to minimise downtime of internet access to prevent the afore mentioned rioting plus I depend on internet access to earn a living.

I especially want to leave the VOIP hub and home automation device hub on the old router (they only need internet access), move the NAS to the main Deco M5 LAN port and make sure the M5 DHCP does not assign IP addresses that conflict with the VOIP hub and automation device hub. The M5 DHCP can give the NAS a new static IPv4 address. 

I cannot find any youtube video or other online information that gives me the all the details and options for router mode configuration complete with screen shots. I get it that TP-Link want the smartphone app to be so intuitive and easy that you don't need an instruction manual, and I think this is as successful as can be expected, but in my situation I want to "design" my solution before I do it to minimise downtime.
 

Is there any info online that can show me what I want to see?