There are still people not into FDM that could profit from it so there is still a market:

1. Run a local business that offers quick turnarounds. e.g. send it before 6 p.m. and production will start before 8 p.m. same day with early morning delivery if possible: The engineer finishes a design in the afternoon and has it the next morning on his desk ready to go. On your end it means once you get home do a little work. Sleep and deliver the order on your way to work.
2. The next strength is service. You run it. You know the process. You can guide them and answer any questions they have.
3. Offer basic CAD design work. This allows you to catch customers who have ideas but not the required knowledge.
4. underpromise, overdeliver
5. If you are into CNC milling offer hybrid manufacturing. Gain excellence and you have some very valuable knowledge.
6. Don't take money out of the business at the start. Build up a reserve for the rainy day that will come (!!!) and keep reinvesting in new capabilities or improving your current offering. Once you reach a decent machine park pay yourself. Don't forget to dedicate some funds for experiments: Keep innovating as otherwise you will fall behind and some new guy that's hungry will replace you.