Welcome to the community.
I believe Diablo 3 requires a Battle.net account but you should be able to use your PC one with no problems. I think uPlay accounts are optional but it has been a while since I played one of their games.
The community isn't really toxic because not many people talk any more. You get the odd kid screaming in games like CoD or some ass blasting music through his mic and some people using their Kinect causing their game sound to echo and makes all their background noise heard but that is what the mute button is for. You should be able to make friends easily enough if you start having fun with people online. I have made about 15 from Sunset Overdrive and several more from GTA and Titanfall. Even if you can't seem to hit it off with anyone, there is a weekly/monthly (can't remember which) friend request thread to post in on the sub.
From my personal experience I would reccomend the connect for the voice controls alone. Being able to turn the Xbox on, control things like volume or load up dfferent games or apps without having to pick up a controller is awesome. Not many games utilise the Kinect as their core gameplay element. Their is fitness apps and sports games that the Kinect is used for and it works reliably well most of the time. Fantasia: Music Evolved is excellent and is worth buying if you get a Kinect. Games like Forza Horizon 2 allow you to use voice for the GPS and an occasional game is released that is Kinect based.
World of Tanks is not currently on Xbox One and I am not sure if it has been confirmed to be coming yet.
I don't really have any reccomendations, any TV will suffice and it doesn't need to be a super fancy curved or smart TV. I hear that playing on a monitor can give a better experience for multiplayer games but I much prefer a big 40" TV that I can just play from the couch with.