Crowds didn't interfere any more than any other crowded site - Disneyworld for example. Just lots of people and hard to take photos without someone you don't know in the picture. You are not shuffling along in a line or anything like that but there are just a lot of people around. We could see things that we want to see at our own speed but you are definitely not alone.
Staying at the hotel at the entrance is expensive but it saves a lot of hassle getting to and from the site via bus. Some commented on the bus ride up and down as being a bit scary. Rough riding and no guard rails. A bit of a challenge when two buses met but no evidence that any bus ever went over the side.
Be sure to bring at least one hiking/walking stick. I could see a small problem if raining or recently rained and wear substantial hiking/walking shoes. Not a place for flip flops or lightweight sneakers. Lots of uneven, slippery rocks. You don't need hiking boots but a good hiking oxford/shoe is recommended. There are no restrooms or trash cans inside the site so plan accordingly. We had heard that plastic water bottles were prohibited but saw no evidence of them checking for that. We carried a plastic water bottle in an open sling over the shoulder with no questions asked. It is a magnificent site that is almost overwhelming in size. We spent a full day inside but another day would have been nice just to circle back on some areas. Since we live at 6500 feet, altitude was not a problem for us but for some people it was.
It was much hotter than we anticipated. At that altitude and early Spring (early Nov.) we thought it would be much cooler but it was warm and with all the climbing you get pretty hot. Very little shade anywhere so if the sun is out it will be hot.
We were very lucky. Just as we hit the train station late in the PM of the second day, it rained hard. If it was raining that hard on top it would have been miserable. Bring an extra SD card for your camera - you will need it. Every step is a "Kodak Moment." Good luck.
PS -- Use a good bug spray. Got a couple of nasty bites before we applied it.