I have Asus Z170-A (Skylake) computer, I assume this will be more than enough to provide the needed USB power it requires? I read that it needs 3 USB3.0 and 1 USB2.0 so it'll require me to unplug something while I use it I think.
Not sure on this, you'd have to research your specific motherboard and find out how many USB3-compatible controllers it has. The recommended max is two USB3 sensors per controller.
Unless your mobo is shit hot, the best you can probably hope for is two sensors on USB3, then the headset itself and third sensor on USB2.
You can get PCI USB3 cards if you want everything hooked up via 3, but the whole setup will work fine on 2 if you want to get it now and improve it as you go.
Here's the oculus blog post on the subject.
How hassle free is the setup? Is it easy to disconnect the headset when not in use? I have 2 monitors, 1 tv and then Oculus would be 4th display device connected to GPU, don't really want to have that many running at all times. Also I assume Displayport to HDMI cables work with Oculus?
I plug mine directly into the HDMI port, but I've seen reports of it working fine with both DisplayPort and DVI converters. Mine's been plug-and-play thus far, so if pulling cables works for you, you can do it.
Is the headphones easy to detach and what kind of headphones can be worn over it? I have Fostex TH-X00, can I use these with the headset?
The headset comes with a little plastic screwdriver thing that you can use to take them off if you want to use separate headphones. It'll output via whatever audio device you tell it to in windows so there's nothing stopping you on the software side.
They're really nice though- being able to just put the headset on, grab your controllers and go is so much more convenient than having to mess around putting on a separate set of cans and worrying about extra wires that can get caught on things.
And lastly is it possible to play games that don't support VR in anyway with the headset? Say Overwatch, PUBG and upcoming Destiny 2, maybe through virtual desktop or something? I understand the experience will be subpar but just kind of thinking maybe it'll be cool, any thoughts?
You can use Bigscreen Beta via SteamVR to play stuff on a 2D virtual desktop.
If you're after a full-on 3D inside-the-game experience, it'll be a per-game thing. There are tools out there to finagle VR into various non-VR games, but it'll be hit and miss depending on how a given game implements things.