I personally using 1TB 2.5" USB HDD, but if you dont need much space you can use even USB Flash memory.

Not to my knowledge but I tried using only one USB port and it worked some of the time. Most of the time it didn't, though.

Yeah, I play games directly off of my external HDD using a Y cable sometimes, and I've never had an issue with it. You can use an HDD with an external power source, but the Y cable is easier since that's one less cable going into an outlet. You have to plug the HDD into the Wii U's USB slot anyway, so you might as well use the one right next to it.

As far as size goes, unless you got started really late and plan to go buckwild on exclusive games in the eShop, you really don't need much HDD space. I have a ton of indies and some retail games downloaded, and I'm only using about half of the 500 GB drive I have.

It was a fantastic price so couldn't refuse. A great purchase tobe honest because with Wii U being so unpopular I was having trouble locating certain releases in stores. You don't have such trouble with the E shop and a ton of memory to fill :)

I'm using ordinary USB-HDD.
Probably Seagate or WD.

thats dependant on the drive you use.. so no.. you might need it.. you don't "have to"

Which drive do you use?

a "freecom" (don't ask.. i got it from a customer) 2TB USB3.0 drive.. it would have worked with just one plug if the WiiU had USB 3.0 interfaces
Now i just use the backwards-compatible extra power-plug thing you got with it.

i had a 200GB USB 2.0 drive that self-sufficient with 1 plug also.. but it got full pretty quick. it was terrible (USB 2.0 is)

Something I forgot to ask that I am curious about: How much space did you end up using?

Something I forgot to ask that I am curious about: How much space did you end up using?