Yup we loved the irony of Stairway to Heaven! But there are no rules (except in religious funerals). You could have the whole ceremony full of music if you wanted, or rather if the person who had died had insisted. You could have it at the house or an open space, then nip back (or not, your choice) to the crematorium. Americans tend not to attend the cremation. Another band would be Christian Death, that would be a fun band to hear from at a humanist funeral.