A much easier alternative is using a different camera app. Did you find this thread when checking whether your question was already asnwered?:
Basically, a lot of apps haven’t been adapted to the new Android security model. Using apps that correctly request SD-card access works around the problem in the meantime.
Nothing is stopping you from copying music onto the SD card when it is connected to a computer. Most apps will be able to read these files from the SD card - it’s writing that’s the problem.
As for storing apps themselves; there’s no way to set the default install location to the SD card. Some apps can be moved there, but I would not recommend it, as there are plenty of complaints about ‘disappearing apps’ - which happens to apps on the SD card for instance when the SD card is accessed from a computer.