Intermittent Internet down - possible solutions?

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I have U-verse 75mbps Internet and every 10-20 days, I completely lose inte
rnet access. The only remedy is to reboot every device (gateway, air tie ex
tenders and most devices) AT&T has been out a couple of times, replaced the
 Pace gateway, and thoroughly checked the lines.
Here's where I think the problem lies: I am building a smart home and there
fore have 39 Wi-Fi devices connected. They are: wall switches, outlets, bul
bs, Google home minis, thermostat, 2 laptops, desktop PC,  tablet, 2 Androi
d phones, 3 Roku streaming players and more. The last tech that came said t
hat my line speed is enough to handle those devices. However, most connect  
at 2.4 ghz because the bulbs and switches do not make use of the 5ghz band.
 I think that even though my gateway should in theory handle all of them, I
 have a feeling that there are intermittent data crashes which mess up ever
Now, I do have an unused dual band Netgear router which, connected as route
r behind router, may help solve the problem. However, setting it up with DH
CP and a separate IP addressing scheme may create more problems as all of t
hese devices must be able to see each other.
Should I put the Netgear router in bridge mode or use it as a repeater? Thi
s is a weak area of my expertise. If there is a good solution using this ad
ditional router, I also need a link to step by step instructions on how to  
configure everything as I don't want to crash the whole system... I'd be le
ft in the dark...literally ?LOL?
Thanks in advance for any advice.

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