You're never going to get realistic ERP software out of a database program. You could get closer with SQL but Filemaker all by itself is not going to make that happen. It's easy to fall into the trap of trying to create the big brain be all - do all package but this approach will eventually collapse under it's own weight and complexity.
That being said you can get a lot of useful help out of simple databases linked together. If you spend a little bit of time on this yourself you will soon learn the basic rule of database development is that you don't have to be terribly smart, you just have to be slightly smarter than the guy that hires you.
You do, however, get out of it what you put into it. If you are willing to go deep you will get more utility out of the program. This does take a commitment of time. It almost has to be a hobby. A well informed vision is really helpful. Filemaker is conversational. Anything you can imagine you can write code for.You have to really understand the business you are coding to get the most out of it.
Job costing & estimating projects is one component that Filemaker does well.
While bean counting is important what you really want to use it for is to help you lower your costs. Properly formatted, database can help you transition to a lean manufacturing company.
Think about the crab boat fisherman who makes $80K in the first month of the season but $30K for the year. A well built database can keep this from happening.