I don't understand what you really have here. Do you own that Arris Surfboard or is that what you are renting? If you own it, you don't need to be renting anything from Comcast. You can just use that Arris as your modem/gateway, connect your router to it, then connect your computer(s) to the router.
FTR, I have the previous model of that Arris and that is how I have my network setup. Though I am using Cox, quite sure Comcast cannot force you to rent their modem.
I lease their gateway but I bridged it so it is only a modem to which I attach my router.
I was wondering if I could lease or buy my own modem and what kind I should get for Comcast.
It is hard to find the most current modem and I thought the one in my attachment might be a possibility
I was wondering if I could lease or buy my own modem and what kind I should get for Comcast.
Why would you lease one when you already are leasing their gateway device? Note it sounds like their gateway device is a combination modem/router/switch. Those are common. But you don't have to rent/lease their devices. You can buy your own which is something you should do if you will be having their service for awhile.
Here is a list of compatible devices you can use with Comcast.
The main thing you will have to remember is once you connect your new modem, you will have to call up Comcast tech support and have the new modem authenticated. This is an easy process. You just provide the new modem's MAC address (and probably your Comcast account information), and they do the rest. You will probably spend more time on hold waiting for someone to answer than it takes to get the new modem going.
The MAC address will be on a sticker on the modem.