Luis, I will give candid advice, and don't take it wrong:
1) You use the words "command" and "lead" too often. You need to look at it as "coordinating" and "supporting". A ride field Marshall will turn off more people than it brings in.
2) Stop using D and C in your descriptors. A D is barely passing, and the only one short step above F. Find a different name for it.
3) Giving your racing advice to new riders is putting a cart far in front of the horse. People just starting aren't focused on racing, they are focused on enjoying the rush and improving. Don't overwhelm them. If you are trying to give pointers, keep them short, simple, and don't overload. If someone asks for your feedback, give it. If they don't ask, don't give it unless they seem open to it.
4) If you intend to ping pong front to back constantly, that is more discouraging than helpful to the people plodding along. It can easily be construed as showing off, and be demoralizing.
5) Pick one or two courses that people can get to know. Don't surprise new riders with a different course every time. As the course gets to be routine, it lets you hang back with new joiners if they need it without worrying about the course. People worrying about getting lost is stressful to them, and repeating courses lets people gauge improvement, and plot strategy.
6) Don't give prizes, or rewards, or post results. This is just my opinion, but since it is no drop, everyone gets back to the start point together. Just talk about the ride for a few minutes, say "Good ride, guys", and move on. It solidifies the memory and encourages camaraderie that encourages folks to come back.
7) Don't adjust anyone's front derailleur.
And most importantly:
8) Listen to your fiance. She will give you the best feedback on how what you are doing works or doesn't.