This was one of our favorite parts of our trip to Maui. The sunrise is truly a magical experience, definitely worth the 3 am wake up! Picture do not do it justice. We went on weekend so, it wasn't too crowded. As the sun was rising the travel guides sang a traditional sunrise chant, which made the experience more special. It is really cold in the summit, so bundle up and bring gloves. It was close to 30 degrees F and even colder with the wind. The biking company does provide windbreaker jackets and pants and fleece jacket if you need. I would take advantage of that if you already don't those.
Now for the bike ride down -- THAT WAS SO FUN! We are not bikers at all (the last time either of us rode a bike was 10+ years ago) and it was not an issue. It is all downhill with 1 or 2 small up hills, you can easily push the bike up those hills if you wish. The views biking down are amazing. Also, you are biking down areas with local traffic so you just have to be aware of your surroundings and follow normal traffic laws.
If you are going to maui, we would definitely recommend.