I have a good friend who is currently an Honor Guard trainee (4*), and based on his experiences and my own observations, I can confidently tell you that the first year of HG here is
nothing like JROTC or CAP (I used to be a CAP Honor Guardsman so I have firsthand experience in the latter case). Honor Guard is probably the most challenging organization a freshman can join here at the Academy. The whole first year is essentially a tryout in which you are tested physically, militarily, and mentally. Honor Guard practices every day Mon-Fri (I think they train for 2 hrs/day), and strenuous physical training sessions for the 4*s are frequent. Honor Guard also has a separate Recognition ceremony in addition to the one for the entire freshman class.
There is also another organization, similar to Honor Guard, called the Sabre Drill Team. The Sabre Team performs sabre drill routines (quite spectacular to watch) in official functions, and also serves in certain ceremonies in which a sabre cordon/etc. is required. I am friends with several 4*s training to join the Sabre Team, and from what I've heard, the Sabre Team experience is similar to Honor Guard in many ways. Practices occur every day, and 4*s are also subjected to physical/mental training like in Honor Guard. The Sabre Team has a separate recognition ceremony as well.
The good news is that anybody can join either program (but not both). All trainees go through the same difficult program whether or not they have prior experience. Additionally, the program is only open to incoming 4*s (i.e. you can't join as a C3C). I believe that all of those who complete the first year of training successfully are then accepted as team members.
As far as ceremonies, Honor Guard is responsible for raising/lowering the flag, funeral ceremonies (such as the firing team) when applicable, and rifle drill performances. I am sure there are many other jobs they perform as well, but I will defer to an Honor Guardsman (or someone who knows the program really well) to answer your question more completely.
Good luck as you prepare for USAFA. Keep focused and don't get hurt.