A suitable tribute?

Being a tribute band! How cool would that be? How would you decide who to emulate? I was wondering about this and related questions while I watched AbbaLive tonight. Do you need a physical appearance similar to the star? I have a friend who looked, at one stage, a little like John Denver (was I the only one who saw that?) and I think I looked like Elton John once too.  Is that enough for the kernel of an idea for a tribute show? The two Johns! Although we might need a better title or name change here in Australia because of the "John" thing.  And, as someone has now suggested, an ability to sing would be a bonus! Does this mean lip-syncing is not allowed?