So i'm just gonna throw a few things out here: You likely won't make use of the current meter, GPS, or GoPro till you get the controls to a point where it's starting to be easy for you. What you DO need is battery voltage in your OSD, and a beeper. The beeper will remind you to land when you are to preoccupied to notice, and it will help you find the craft after a crash. As far as your antennas.... that's a little bit of a hot mess sir. It's ok, most of us break all of our parts a few times as we learn. As you do repairs you will find ways to mount things that work better/are tidier.
VTx antenna: so mounting it straight up/perpendicular to your top plate is VERY convenient, but there are some downsides: carbon fiber is conductive, and we don't ground to the frame like you would do in a car, computer, or house. If your antenna mount is grounding your video system to your top plate it will likely give you some signal issues (static in your goggles, or other video problems). Your question about mounting it at an angle is headed in the right direction. Basically you need the mount itself to be flexable, so the antenna doesn't shear off in a crash.
As far as 3s vs 4s: I know that I didn't fly fast enough to take advantage of the 4th cell for at least a year, but I didn't use a flight sim much for the first 2 1/2 years (I would change that, if I could go back in time). You can really learn a lot in the sim. I definitly bought and destroyed a good half dozen batteries before I was good enough to take advantage of the extra power. I would say buy cheap 4s batteries. They will likely have crap output, and some of the cells will die early, but for less than $20 it's hard to care. They will fly like a good 3s battery. The ONLY thing you are likely to be able to enjoy about a 4s over a 3s are these 2 things: big saves, and big punchouts. If you are doing a maneuver and things go wrong, 4s allows you to save yourself without any forethought, you can just jam the throttle, and the power is there instantly. You will likely enjoy the impressive speed of a full power punchout on 4s, it's addictive. It's also impresive to watch, so if you bring a friend out with you flying you will flex it at least once, just for the shock value.
Get out there and fly, every day that you can. Here in the USA legislation will likely take the ability to fly something like this away from us, as we will all have to get in under 250 grams, here in a year and a half-ish. Take this bird out and fly her every day that you can, it's an INCREDIBLE experience. There are few of us here on earth that will ever know the thrill. It's like being an electric hawk.