I'm a bit more familiar with the AWI period, but I think some more general statements could still translate. So, Sharpe is a fun series, but one must remember that it is also "Hollywood."

I think your question comes from a generalized stereotype, one that may have a kernel of truth into it, but far from complete fact.

So a bit of background. Like in another post, I mentioned social class distinctions. The British had a social hierarchy that also applied to their military. The rank and file mainly came from the lower classes, like laborers, while officers (commissioned) came from the gentry, or even doctors, lawyers, landowners, and wealthy merchants.

Could you explain what you mean by relationships between the three? As in interaction?

As for competency, well that depends? Non-commissioned officers, sergeants, came from the ranks through merit. Officers purchased their commissions, not to say that a few officers didn't come from the ranks but that wasn't as common as one would think. Formal military training wasn't required, but there were plenty of "manuals" and treatises on the subject available. I have a few documents that list out baggage of officers in the AWI that show some of the younger officers had some copies of these books. However, that doesn't always mean competency. If one had the money and the right political connections, one could purchase a majority or even a colonelcy. However, I would not say this was true for all officers, one could get promoted as a reward as well.

Steve Brumwell's "Recoats" would be an interesting read for you, though a different period.