I have been to 3 DEs (6 days) so I'm not an expert, but I'll give you my thoughts until someone more advanced responds.
Different regions appear to have different rungroups. In Memphis, we have novice, intermediate, advanced, and instructor. The StLouis
PCA had those and one more (which I can't remember). After you have enough experience and your instructor is comfortable with you, they will sign you off to solo. My understanding is that once you are signed off to solo on a particular track, you can solo for future events. An instructor may need to verify your competence before letting you solo at a future event (this part is unclear to me).
I have moved very quick through the ratings. The most important thing to remember is that you need to be comfortable with the advancement. In my case, I spent two DEs in novice and was promoted to intermediate. After another DE, I was signed off to move to advanced. That said, I can't say that I am comfortable running my CaymanS in that rungroup yet. Rules tend to be very strict on passing in novice. They lighten up a bit in intermediate. They lighten up a lot in advanced. For example, they will designate certain areas of the track for passing. They may say that between turns 3/4 and 1/2 are passing zones for novices. They will add another area or two for intermediate, etc, etc. Although they aren't supposed to, I've seen advanced drivers passing in the corners, which I am not comfortable exposing my CaymanS to.
I was told by my last instructor that any student may run in a lower class. I've registered for my next DE as advanced, but will run in intermediate if I become uncomfortable. I would strongly recommend getting an instructor with a Cayman or a Boxster. I learned more in my track time with Dan (STLPCA), than I have in either of my other DEs.
Anyway, hope that helps FWIW.