In my 2018 Forester XT Limited (Canada), I just paired my iPhone with the stereo, told the stereo to use my phone as a phone and also as a media source (I think, I'm not in the car now) and everything else just happens automatically. Contacts are transferred (I have a few hundred) and contacts marked as "favourites" on the iPhone are displayed in the speed-dial menu on the stereo. You can also scroll through the contacts in the stereo and mark each one as a speed dial or not a speed dial.
It does take some time for music playlists and other phone info to load over Bluetooth, so when you have a black screen, it just may be taking some time for the stereo to process it all.
For the text messages, press the envelope icon on the stereo and do the setup in there. Again, I'm not in the car right now but it's not hard to find. If the car is stopped, the incoming text message will display on the screen, but if the car is moving, the screen will display a safety message instead and the incoming text message will be read out to you over the audio system. You can also dictate outgoing text-message replies, but you have to have Siri enabled for this to work and I turn all my Siri off so I have never explored this functionality. Importantly, to get the incoming text messages to work, you have to go into the iPhone Bluetooth settings and enable "show notifications." There are some other things in there you will want to enable as well, but you won't get the incoming text messages unless you have the notifications enabled. I think without the notifications enabled on the phone, you will get that "round and round" problem.
I never got the incoming email working on the car, and didn't pursue it.
This is with the 7" screen stereo that comes with the car. The navigation system is quite poor and I want to change the stereo one day, to one with a decent navigation system. In my previous car I used to clip my iPhone to the dashboard and use the phone for everything, but started using the built-in navigation with this car. But the car thinks I'm about 100 m behind where I actually am, so if it tells me to turn left in 100 m, I'm already turning left.
You do not have to have any Subaru apps on your phone for any of this to work. I am using an iPhone 6.