is there another level of middle mgmt between Caporegime and foot soldiers?

Nope. Usually not formally anyways. Of course, like any other organization the formal titles don't necessarily indicate someone's power. Soldiers can vary widely in their income/power. Some soldiers are "specials" and have so much knowledge or experience in a particular criminal endeavor that they more or less report to the Family's administration.

In other cases a captain may rely on a handful of soldiers he trusts to transmit orders, enforce discipline, and collect funds. But it all comes down to money. Over time, all else equal more "respect" and "power" will accrue to those soldiers who are better earners.

As Lilo said, it varies by family and by size. I'd imagine that, in a big family, caporegimes would have crew chiefs under them to help manage the business. A crew chief might, say, have 5-15 soldiers under him, and a capo might have five or so crew chiefs.

Lilo, I see you changed your avatar to Chester Burnett. Good man!

Thx!
Who better to discuss how to Commit a Crime than the Back Door Man himself...

Capos are definetly the next level from soldiers however there are different variations. For example when a crew boss goes to jail they name one of their soldiers as acting capo who runs the crew in their absense but they are not an official capo. Ther are also soldiers who act as a liuetenant to his capo like Angelo Ruggiero was to Gotti