You say multiple 1000 miles. Crossing borders? Then be careful with the phone. But if a phone and just stored music any head unit with a connection for the phone will do. Or a Bluetooth speaker. I like the JBL ones as you can link them for left and right.
Yup the plan is to drive up as close as we can get to the artic circle so we can see the northern lights as its something I want to do before I die, a bit strange I know but it will be one off the bucket list.
Shooter
Ok so the phone would be more if the storage device for the tunes rather a streaming from data.
there are a number of Mini clubs in both Norway and Sweden and I know of a few Mini specialists in Sweden that stock parts.
all I will say is standard height suspension and no low profile tyres many roads are not tarmac. If you do winter you will have to have Winter tyres. Get mossy replant when there. It is a very long country.