What equipment to use if supplying my own

Hi everyone,

I've been having the toughest time with comcast and getting the speed I'm paying for, I have 2 houses both with brand new equipment to handle high speed and I'm not getting even 1/3 of the promised speed, those are still pending troubleshooting, which leads me to this next question, I have an installation tomorrow at a 3rd house, I'm tired of wasting time and money with all these issues so I would like a recommendation of what modem and router I should get and if it's better all in one or separated, the installation details:

- House is Oak Park Michigan (48237)

- Paying for 300mbps (I think it's 20 upload)

- will connect directly a smart TV and a NVR recorder (3 security cameras), 2 smart TVs wireless

I know I can get top of the line equipment but this is not a house I want to spend $400 for a router/modem. So to get the 300mbps speed what do I need?

1. Is docs 3.1 necessary? Should docs 3.0 give me the 300mbps speed?

2. Do I need 32x4 channels? or can I achieve 300mbps with 16x4?

(by the way, in one of my other house installations, I have a motorola modem/router MG7550, on the Xfinity recommended list, that can support up to 600mbps, docs 3.0 and 16x4 brand new, there I'm paying for 300mbps as well but I'm getting 120mbps in the 5G spectrum, in the regular getting abot 57mpbs, the installer said it's because it's 16x4 which basically it's halfing the speed, called motorola and they said the installer is BSing me)

3. What brand and model of modem and router (under $300) do you recommend to achieve close to the advertised speeds? separate or all in one?

Thank you in advance!