Shum...
I don't have much experience with the big MRO types but the ones I do know about employ between 100 to 270 workers. While the 145 rules are the same for all each one can be different based on their ratings.
FAA issues two different certificates and one authorization that allows an individual to sign off work on aircraft: A&P Certificate and Repairman Certificate, plus the Inspection Authorization (IA). All three can be used under a 145 operation, but only the A&P and IA can be used outside of a Repair Station (RS).
How the certificate privileges are used under a Repair Station (RS) is determined by the FAA approved Repair Station Manual (RSM). In the case of Repairman Certificates, The FAA allows and approves the RS to develop their own Repairman program which is documented in the RSM. Normally there will be a separate program for each specialty: airframe structures, powerplant, avionics, composites, welding, NDT, QA inspector, etc, etc....whatever the RS needs to accomplish and sign off. Each program usually has a minimum experience requirement, etc that an individual is required to meet before it can take the RS Repairman Test. Once the FAA approves the RS request for an additional Repairman, the person takes a test and when passed the FAA will issue the Repairman Certificate.
Normally there is a more pronounced Quality Assurance component within a 145 RS and they normally are required to sign off behind any work a Repairman or A&P signs off...whatever the RSM dictates.
The RS also has the ability to use non-certificated people and does so usually at a ratio of 1 Repairman to 10 workers, with the Repairman signing off behind any work performed by his "crew"
A lot of the smaller RS use A&P's especially if the RS is affiliated with any type of a 135 Ops just because it provides more flexibility with personnel.
If a RS does work for a Part 121 or 135 operator then they must also follow the operators maintenance manual requirements and if those require specifically A&P or IA individuals then the RS must supply those people also.
There really is no set structure for manning a RS. Just depends on what you want to do and what the FAA approves you to do.
Here is some dry reading that may give some more insight...
http://www.faa.gov/documentLibrary/m...%20CHG%201.pdf
http://www.faa.gov/documentLibrary/m...C%20145-11.pdf
w1