A total of 2 reviews of this product on Reddit.
4: I think you made this more difficult than it has to be and I will try and explain. The mixer is the audio capture device while the AVerMedia/Blackmagic is the video capture device. The only reason you even need a mixer is to capture multiple audio sources that you can manipulate the audio with little latency. Ive seen many setups where a mixer is not even needed, especially the ones that are just being used for a single mic. Keep in mind that if you are using professional mics with xlr connectors, you will need some way to interface with them (audio interface).
Above I mentioned the reasons why I chose certain capture cards and one of those key reasons were an audio input. I didnt want to have to deal with syncing audio in OBS. The streaming pc uses the capture card to get video and audio into OBS then stream it to Twitch. You can go as simple as splitting your audio from your gaming PC (one side headphones/speakers, other side goes to capture card) and use virtual audio cables to even send your USB mic. Bam, all audio done and no need for a mixer.
You want to up the anti and have more audio devices going to the capture card or a xlr professional mic, get a simple mixer. You dont have to go Super Saiyan and can find plenty of really good 2 channel mixers for under $50.
You want ultimate control, turn knobs like a DJ, and get the audio into a pc digitally? Then get something that has an audio interface, like the Focusrite Scarlett 2i2 for example.
I personally use the Steinberg UR28M (http://www.amazon.com/dp/B005OQ4N7Q/) for a couple of reasons. I have an XLR microphone, I wanted a portable all-in-one audio interface solution, I have no need to manipulate the audio coming in other than levels (volume), and the software that interfaces with the Steinberg is exactly what what I wanted in order to manipulate the audio without having to own additional hardware. The UR28M also functions as a soundcard and I plug my headphones into it directly to hear everything that goes to the capture card. My only complaint with the UR28M is that for whatever reason they only decided to mirror the audio from the USB on one Mix track. This makes no sense and even on their forums people have been dumbfounded as to their answer on why.
I hope that made it easier to understand. If not, here is an image of a mixer with audio interface (https://i.imgur.com/WW21vhn.jpg). In this setup the xlr mic is going into the mixer via xlr, the gaming pc is sending audio out the speaker jack (3.5mm), all the output audio is going to the streaming pc via USB, and the headphones are plugged into the mixer to hear everything.
5: I use a Rode PSA1 Mic Boom and it still gets in the way. This is only because of the mic I use (I have to be right up on it). You could always use a different mic, shotgun mic for example, to pick up audio out of frame.
6: This is all about the type of mic you use. Different mics have different pickup patterns. Think of a concert, there are speakers that point back to the artist so they can hear the music without the mic picking it up. At the very least, most people will use earbuds to monitor their audio.
As for your last part. The only reason people are “reinventing” the wheel is from ignorance. Seriously, this equipment/idea has been around for a long time. There have been hobbyist radio DJ’s for years doing this way before Twitch. Now we are just upping the bandwidth and sending video. The only thing that has changed is that the hardware is so affordable that there is no excuse to not give it a try. The reason OBS is as popular today with the Twitch community is because it’s free. There are plenty of other full featured software packages that larger companies use that are well worth the price.
I have the AT2035 XLR mic. Super similar. My setup:
Mixer/USB Interace: http://www.amazon.com/gp/product/B005OQ4N7Q/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
I had a Behrninger 5-channel mixer first, but could not stand the low hiss in the background.
Pop Filter (Doesn’t block your whole face): http://www.amazon.com/gp/product/B00946ZJN4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1