It's been almost two years since I was there. I only did about 11 miles south from York so my info my be totally wrong. I think the surface is like most other official trails, fine stone rolled down. I think the 32s would be fine the 23s maybe not so much.
My wife and I have been on it twice this year. Road bikes are not uncommon on the trail. We started at Brillhart Station and went to New Freedom. Two sections have a bit of a soft surface after repairs to washed out areas. Otherwise the surface is fairly hard. Last year we did two rides down into Maryland. We found the trail surface to be fairly hard. Looked like a fine sand rather than the limestone "stone dust" used on the PA section. I was running 700 x 35 c tires on my Multitrack and had no problems.
The trail head in York is not too bad of an area.
At Seven Valleys there is a nice snack shop in the old railroad station. Benches and tables for a rest and very good ice cream. At Hanover Station there are drink machines and rest rooms. At Glen Rock there is an old mill converted to a restaurant. Across the street is what looks like a little pizza place. It actually has a very fine Italian restaurant in the back. Good food at reasonable prices. Then at New Freedom the old railroad station was converted into a small lunch room and museum. On the Pennsylvania end of the trail there are numerous benches and roofed over picnic tables along the trail.
Once into Maryland these places are fewer in number. So before you go into Maryland you might want to stock up on fluids if it is a hot day.
Both the PA section of this rail trail and the Maryland section are very rural in nature. A lot of nice pleasant people on the trail.
When we did that trail for the first time we passed by the converted grist mill. Those sneaky devils have the kitchen exhaust hood blowing right over the trail!! A good meal was out of the question given the ride back to Brillhart Station. So we then started to do the trail from New Freedom to York. That way we could get a good meal AFTER loading the bikes onto the car at the end of the day.
Reporting back. We did both the trail from York down to Monkton MD. The Pennsylvania section did have small gravel,but not much, we had no problem on the trail at all. The Maryland part was hard packed dirt, no gravel at all, we made much better time. All in all an excellent trail. I'm not sure how it would be if it had rained a lot, we were lucky, the weather was beautiful and the trails were totally dry.
Also on PA side, good stops, though the New Freedom cafe was packed and it seemed all the other restaurants in the town were closed.
Excellent ride on both the road bike with 700x23 and the very loaded touring bike with 700x32 tires.