I'm with a few agencies, Alamy, PSC and a couple of flower/plant ones.

If you're looking for a way of funding new gear... you'll need 100's if not 1000's of photos on the libraries. As well as a good dose of luck!

Agencies will take between 30%-70% of any sales you make through them.

Any agency worth it's salt will want to see your work before they allow you to join. So be prepared for lots of refusals at first.

But, keep at it. If your photos are good and saleable you'll get in. Best of luck