Need a Comcast modem to support 2 ethernet PCs and WiFi

Just got home from the Comcast store with a $7 rented modem just to last me until I do research and purchase one. I realize that this modem has only one Ethernet port with no WiFi support so I have another PC and a laptop sitting idle because there's no internet access. Did a quick search using Comcast's authorized modem's list and all of them only have a single Ethernet port and no WiFi. Is there a modem with multiple Ethernet ports with built in WiFi?

I am getting almost 20mbps with a download speed of 4mb/s which is a HUGE improvement over my ATT DSL service that I've had since forever at 3mbps with a download speed of 300kb/s. I have no idea what technical specifications to look for in a cable modem to get 100% of full potential speed from my service without disconnects or other various problems.

I have a ATT U-Verse router sitting here right now, I am wondering if I can somehow connect it to my Comcast modem. I tried to connect the ATT router into Comcast modem via Ethernet cable, but I couldn't get past the "Your DSL service is unavailable" in the browser, but in my desktop system tray, it shows I am connected to the internet. If I could use this router, I would rather spend money on a modem instead of getting a combo.

Also, if such modem/router/wifi exists, would it give me worse performance compared to 1 single modem into 1 router?

Thanks.