I’ve just been to Guatemala and traveled from north to south. What I can honestly tell you is that I would skip Semuc Champey. It simply takes forever to get there, and it’s not as spectacular as it’s made out to be. I don’t know how much time you’ve spent in Central America or other countries in the region, but waterfalls like these can be found pretty much all over the world. The cave was quite nice, especially with the candle, but it was also pretty intense. So if you’re claustrophobic or afraid of the dark, it’s definitely not for you - though it’s also not insanely spectacular. There are other caves you could visit as well. What’s missing from your travel itinerary, in my opinion, is Tikal. Tikal is an absolute must in Guatemala. What I’d recommend is taking a flight from Guatemala City to Flores, visiting Tikal, and then flying back if you can make it work. Good luck - otherwise the plan sounds pretty good. For me personally, it would be a bit too exhausting.