If it were me I think I would connect the data to USB DAC-UP. (I just looked on the sockets and all four pins are there on the Mojo. Though no power goes into the Mojo there.)
For powering the Mojo by USB, it depends if the USB DAC-UP port has enough current to power the Mojo. The Mojo recommended power charger is 1A, but old USB 2 is only 0.5A. (However I thought I read that USB 3 had 1A on the power rails, but I am not sure about this at all.) You need to determine the current rating of USB DAC-UP ports.
No problem either way though. If you need to get a charger for the Mojo, the power should be reasonably clean. I have one of these rated at 1A (Plug USB cable into it.)
As
@Relic
said though, less noise anywhere is better. If you can use both USB DAC-UP ports it would be what you want. If not, it's not a problem. It sounds like you a new to the Mojo or choosing whether to get one. I'd advise you then to read the third post. You will undoubtably come across something you want to know.
Anyway, have fun with your ultra-gaming board. I am a gamer too and use the Mojo for gaming, as well as music. I use headphones and desktop active speakers. (I am currently playing The Witcher 3. The first time I used the Mojo with TW3 I was using my speakers. I noticed that the extra transparency and detail of the Mojo made the sound more realistic. When I loaded up the game I was at a market and chatted to a merchant. It was a nice day sunny day in the game. The Mojo made it sound more like I was out in the open air.)