Is there wavedashing?

Yes, there is. It is easier to do them perfectly, because you can buffer the airdodge in the jump squat. Also turning around only takes 1 frame and all attacks turn you around instantly too (if you use the right control stick), so wavedashes are a good bit less useful (as in: less necessary).

Are there customizable controls?

Yes, press B (gamepad) to open the player menu and adjust your controls. Various input devices are supported via custom mapping and calibration!

Is there be GameCube controller support?

You can use a GC controller by using unofficial drivers for the Wii U adapter (http://m4sv.com/page/wii-u-gcn-usb-driver) or by using the PC mode of the Mayflash adapter. But sadly the Wii U/Mayflash adapter will not work natively, like they do in Dolphin (yet?).

Why can only one other computer  connect to my lobby?

So far the netcode is implemented in a way that only enables NAT traversal to one other computer. If you wish to play together on more than 2 machines (you can still play 2v2 with 2 people per computer each), you need to forward the port 40433 (UDP) manually in your router.