RAX120 Performance Diagnosis

I have installed a RAX120 and an EX8000 as an access point.  I also have an EX7500 installed as a wireless extender using the same SSID as the RAX120.  This network extender is used primarily to improve a security camera and receives very little use otherwise.

Occasionally I am experiencing slowdowns/interruptions in my network. Most of the time, these disruptions occur during the late evening or very early morning hours and seem to last about 5-15 minutes (but I have not tracked the).   I also have occasional performance issues.  Is there a recommended reference document I can use to help be conduct an analysis of my router configuration to see if there is a problem that I can fix.  My problem may also be caused by issues in my Spectrum service and being able to pinpoint the issue might help if I need to call them.

As a side discussion, I am considering increasing my Spectrum network service from 100mbs to their 400mbs service.  Not sure I need it but being able to diagnose performance issues within my network might help with this decision.  

I have 2 Macs (MBP and an iMac), 2 iPad Pros, 4-5 Roku or Apple TV's, and a number of IOT's.  For the most part, they all seem to work well.