This is probably not the job you should be dipping your toe into to see if you like this type of cleaning, using untried casual labour on what is in effect a building site is not a good practice and could land you with more problems than solutions.
We have done quite a few church cleans post restoration work, you will need long reach poles/dusters and long reach vacuums as they will require stained windows to be vacuumed, dusted and possibly washed, also high ledges, hanging lights, lots of carved wood, pulpits etc. Also if there are bare stone floors they can take a LOT of cleaning and washing. Possibly scaffolding as well, pews will need to be moved and cleaned. The last church we did had just been damp-proofed and took 3 people 3 days to clean.