PBJ - the 5v thing may be because a cell phone chargers 5v outputs like 700ma, and the Pi3 needs at least 2ma. I use a 2.5ma unit with mine and no issues.
In regards to setting up on a cabinet - Emulation Station is okay -
but Attract Mode is where it's at! You have a lot more freedom IMO.
The issue I found was trying to get file names to play nice. There is a way to do it in Emulation Station, when you scrape the data, one of the formats will show only the game name, though it's never 100% - depends on the gamelist file that contains all the metadata... I had to edit an entire system worth of metadata because it was the only way I knew how to do it.
What I found next was much easier, and looked better in my case:
Install attract mode on your pi, update everything, and make your own layout using AM builder. What I did was I added all the games to my Pi, the Video Snaps and the Wheel Art. My build fires up and goes into Attract Mode displaying a full screen video snap with the wheel logo overlaid above it. Very clean and simple. No metadata. Almost gives a feel of a specifically built design, but it was quite simple and straightforward.
Here is a link to the AM Builder:
https://goodiesfor.me/attractmode/builder/It outputs a layout.nut file you unzip and simply add in with existing AM themes in its own folder with a cool name for your new theme. Play around in the builder and you'll see its pretty easy to figure out, and there is a 4:3 and 3:4 option. It takes some trial and error, but once you have all your roms and snaps, cycling through layouts isn't that bad.
There is an Attract Mode forum with an FAQ that walks you through everything you need to do, as well as providing links to download (although I think a version of AM is now offered in the optional or experimental packages in RetroPie). I do not want to start a migration, but perhaps a movement where people aren't so intimidated by the Pi and what it can do.
PM me if you have any questions and I ghost on this thread.
(Please don't think I hate ES. I don't and actually use it for console games... just doesn't look as good in a cabinet)
edit: I also want to add that the Pi performs best if the screen rotation is handled in RetroArch, not on the config.txt file on the Pi. If you're going vertical it's worth doing. To do this, make your AM theme sideways - when it loads up "normally" it will be rotated for your vertical cabinet. The up down left right inputs are mapped in AM so when it asks you to "next game" on the config in AM, you pick the directions of the joystick, so it's all coherent. I dunno if this makes sense, but came to me when I recalled Pac-Man is a vert game, dunno if your monitor is tho.