Leti, my office and my library are separate rooms. Some people have permission to go into the library - most of the older kids can, if they have a good reason. It's mainly off limits, because that's where I keep a lot of my more expensive 'toys', do I don't want the younger kids going in there on their own.
The office is a different situation. There are times that I don't mind someone going in there. However, there are also times when both my desks and the coffee table are all covered with work, and I don't want anyone moving things around. That's why you're supposed to have permission to go into my office.
Pi, we have an account with a couple of online sheet music companies, primarily Music Notes, and Van has his own account -he has a debit card now, so they can buy things online.
I dealt with this the same way most of you did. I told him that I appreciated him telling me about it, and that I was very proud that he trusted me enough to believe I'd be fair to him. No spanking. I'm not getting him a printer, since this is mainly him being impulsive and wanting it now, instead of waiting a few hours until I'm home. The problem is that, even if I got him a printer, he'd have to go into my office to use it, or I'd have to change the settings on the kids' study computers, and those are too unsupervised for me to want them to be too open (those are mostly for the younger kids).
One thing I'm considering is a cheap tablet, so he can download the sheet music and read it on the same tablet. He might have to wait until Christmas for that.