1) How many people use Filemaker, on average, at your customer's business? (How many'seats').
Some of my businesses, 5 ; some 500.
2) What complexity of Filemaker systems is usual? In order of increasing difficulty... a) Single table or b) an invoicing system c) a complete accounting system (Billing+ General Ledger +Account payable and receivable) d) A custom enterprise resource planning (ERP) system
Every solution I have ever created has been completely different, from one file for importing/exporting only to full software replacement of almost all of a business's programs.
3) A description of what type of Filemaker work you are typically asked to do.
Work varies: tracking down a break in someone's system, writing a complete solution, helping another Developer, handle migrations, beta testing other programs, integrate with MySql or Oracle ... Some projects take me an hour and some take a few years.
There is no such thing as 'typical' when it comes to working with FileMaker. This is one of the reasons I enjoy what I do - I am rarely bored.