Good afternoon

I purchased a two pack of the TP Link XE75.  I have DSL service with AT&T which comes with a wireless gateway/router/modem in one.  I have worked with AT&T to disable to the gateway/router/wifi functionality so the equipment only functions as a modem and the TP link node connect to it now provides the router and wifi service.  That said, I am expereicing a lot of issues that cause me to reboot at least once a day if not daily.  So with that said, I have a few questions.  

1. I did read a blurb somewhere that there are special mesh systems designed to work with DSL... but I've literally only seen that information in one place so I am not sure I should trust it.  Any insight as to whether Mesh Networks require a specific package to support DSL? If that's the case does the XE75 have DSL support?
2. Is it possible I have too many mesh nodes on my network which is creating the issue?  I have a 1600 sq ft house that is 3 stories - a walkout basement, the main floor, and then a second level.  I have the router node on the main floor and the second node in my room which is on the second floor and the opposite end of the house.  
3. My home is wired with cat5 or cat 6 throughout.  I noticed that when I hardwire the node in my main bedroom the performance seems to decrease.  Why might that be?
4. Finally, is there a chance my house is too small for the second node?  Is there an app or something you can do to measure that to see if there's simply too much going on for a home my size?
5. Can TP-Link help me with the configuration of my gateway/router/wifi modem? AT&T says we've configured things correctly but I don't necessarly know that what they had me do to the configurations is all tha truly needs to be done.

Thanks for your adivece and sorry for all the questions!

LampDL