Why is apple holding my iPhone hostage?

It keeps popping up a message saying "Storage almost full" You can manage your storage in settings. Like I already deleted so much stuff already. Also, why it gotta keep popping up its not even full. Like does it want me to overload the capacity or something? Is there an option to turn this bug off?

If I get a new phone will all of my music from apple music be deleted?

I have a membership for apple music. I know that if you fail to pay, your membership will be deactivated and you'll lose all of your music. I'm planning on getting a new iphone, if I login to apple music on it, will I still have all of my saved artists, songs, playlists, ect? (I will continue paying it on my new phone as well)

Should i buy an iPhone 6S with itune and usb logo on it?

Hi, I'm going to buy an iPhone 6S on ebay, I recently did bought broken iPhones and repaired them and sold them and gained profit, but this one i'm quite unsure. The owner of the iPhone claims that the phone is in perfect condition and somehow he got in itune logo and he dosn't know how to fix it so he bought another one. I know how to fix it, you basically restore it but I'm not sure that does it have any other problems?
So can anyone please tell me any other problems with itune logo, apart from restoring the phone, on iPhone 6S?