For most people, they like to know how many hymns they can have. Three would be the norm, or four if you wish. Again, time is always against us, so we need to be realistic. Also, when choosing hymns, make sure they're hymns people know; and if you know people will not sing, you need to consider whether having hymns at all is a good idea. It can seem disrespectful if no ones singing. So, in this case, the best idea is to have a few pieces of music played on CD at certain times of the service; (not pop music). However, the priest will always try to accommodate your musical preferences.