It will work with online gaming, depending on how much bandwidth the game requires. If it's a 2-player game that really hogs the bandwidth (a couple of the newer games) you might have an advantage with a dual band router. Look for an AC1900 or faster if you want the ultimate in game play. Use a direct connection instead of wifi if at all possible.

Probably not, but that depends on a lot of things. This gateway will download or stream a high definition movie without stuttering, provided you're not using the internet for a bunch of other stuff at the same time. Your 100 mbps service from TWC might be delivering (to your home) less than 20 mbps, which is about what you need to stream a hi-def movie without buffering. You should check your actual download speeds online to see what TWC is providing you in real use. There are a whole bunch of sites that allow you to speed test your service. Just Google "speed test" and try them out--your speeds will vary depending on how rigorous the test is. www/dslreports.com/speedtest is perhaps the most accurate, and it allows you to test for every type of service--for example, "cable".

Yes, built in wifi, all security formats.

That depends on a lot of variables. The obstructions, like walls that you're going through, will affect the range. Other wifi devices in close proximity will also affect the range, and that includes your neighbors wifi. I have a 2 story house with a full attic and full basement, and there's no place in the house that the wifi doesn't reach. The gateway is pretty centally located and I'm not using any beam forming. I have other devices that are close to the gateway but they're all connected with CAT5 cable so I'm not crowding the wifi. I don't have any neighbors houses right on top of me, although I can see their LAN's on my computer. If you have a problem setup, with lots of walls between the router and your device, you can always add an inexpensive range extender, but I've not found that to be necessary in my environment.