I haven't gotten avahi to work correctly on my n900, yet, but have avahi on my n8x0 tablets...
Yes, rename the S14 and ?S16? avahi scripts to S21 (that is what worked on my tablets).
I don't think that I ever modified the avahi...conf file, just my hosts and hostname to give the tablets friendly names -- I don't recall if avahi propagated it...
Never noticed a significant battery drain from avahi/ssh (once again on the tablets).