Once I back up my computer with time machine, can I delete music and pictures and still see them on my time capsule?
Please do not do this.
Time Machine backs up the changes on your Mac.
If you delete the "original" files from your Mac, at some point, Time Machine will pick up that change and delete the files from your Time Machine backups.
There is no way to know when this might occur.
Even if the files stay on the Time Capule for a few weeks or even a month or two.....these will be the only copies of the files that you have. You have no backups.....so if the Time Capsule or Time Machine has a problem, you will lose those files forever.....unless you have backups someplace else.