The Chinese install the app/s of their choice so I go with that, otherwise it would be off the store and have associated adverts.
I've tried many but I'm just lazy now and work with what they provide. But if you find a good one, that for instance shows the rotating disc for easy recognition, I would be interested.
My unit/s use the house wi fi for downloads / upgrades. Tom Tom for instance uses a lot of data when installing the actual maps.
To download Apps, 1st you need to be on wifi, then go to Play Store like you would your phone.
Otherwise the HU is tethered to my phone, when on the hoof, and that's mainly for live traffic.
Android phone becomes 'Hotspot', create your own code / name, HU sees it as a wi fi network.
As said internal mic is useless on the hoof, with an o/h mic I use 'Hey Google' to text and call, and even Tom Tom has voice recognition software for finding places.
For downloading music + to the internal memory 1st find the 'Music' file within the HU, possibly via 'Files'. Then copy from USB / SD (possibly found in 'Storage') and paste into 'Music'. You should see the 2 pages icon, just plain 'Copy to' for that.
You may find that retitling your albums can be useful to create a better order in the HU, it depends how the HU is set up to deal with them.
It sounds like you have only tapped in to only a part of the functions.