My opinion is that it probably depends on the churches you go to. If they think that you share their beliefs and that is one of the reasons you are hired then you should let them know if you are not what they think you are and see if they still want to hire you.

As far as your personal belief and differences with your customers' beliefs, even if you are a professional musician then you should also consider if you are bothered by it and whether it is in great contradiction with your faith. If so, then you should not take the gig. But about the earth being 5000 yrs old, I don't think it's such a great hurdle to overcome. At least they do not ask you to worship something that you are not allowed to (according to your beliefs). If they require you to do such a thing then you should find another gig.

Now, if you are a Christian, the spiritual reference is there in the Bible. Take Daniel in the old testament bible, he served the Babylon king who worshipped a different entity (an idol) but when he was required to worship their idol, he flatly refused. God apparently blessed his life even though he served a king who clearly did not worship the same God as Daniel's.