I've worked in the industry for about 4 years,
Vouchers can be 2/3 days to 2/3 weeks, its all about how quick your employer gets paperwork turned around.
Its a awsome scheme tbh, saving a massive amount on a new bike who can complain? anywhere from 25-50% saved! All depends on your personal circumstances, and you will never know how much it will cost you until you have done all the paper owrk and start to pay sorry to say.
ID wise, we used to only accept work ID cards, driving licence, passport. You really really need something with photo id.
The Scheme only allows you 1 bike per year. With a total cost up to 1k.
You can tho, get a 3k bike and put 1k through RideToWork/CycleScheme and pay the rest off elsewhere but you only get the saving on the first 1k.