Is my internet good enough for streaming on Twitch?

Probably speeds should be good enough, how about ping and jitter they are also important. Use this tool if you want to know: http://www.speedtest.net/

Well, the how much are you really getting question is a tough question.
You know how ISPs are always selling you packages "up to XXX Mb".
Well, the "up to" depends on your location, the quality of your connection and the time of day (or how many other people try to use the same wires as you).
And, some theorize, the position of the moon, the purity of your local pond, what you last had for supper, and your mother's maiden name.

So . . . somewhere between 6 and 13 Mb/s probably.
If you want to be sure gather a whole bunch of data points to different points and at different times of day and then take the 10th percentile or something as a conservative speed.

There's a lot of different information out there for upload speed requirements. Apparently 3-5 upload will get you 1080p with H264 (You will be using OBS?). It's just that you'd better have that 3 as an absolute minimum, not the average speed, so that 6.5+ should probably get you there with some bitrate fiddling.


The powerline adapter.
* There are some different speeds: The AV, which is enough for internet speed transfers, and the AV2, which is a lot faster but unless you're sending large files over the network not really something you'll ever need.
* The ports are easy. The in-port you will require is 1 (router -> adapter) and the out-port depends on how many devices you will be plugging into it, so if that is just the PC you posted that means 1. If you have an XBox you will want 2. But most (all?) of the systems are modular. So I have 2 1-ports now (one at the router, one at my computer) but if I want to add one later for my wife I can buy one and add it to the system or I can change the one at my computer out for a 2 port version. Although I'm assuming you'll want to stay with the same brand when doing that.
* You will likely want the outlet pass through. The system doesn't work well with power strips/extension blocks, so you want it directly into the wall and then plug the power strip into the pass-through. Unless you have a spare socket, of course. Extension chords work fine, but not if it has an internal circuit breaker.