This section is relatively easy (emphasis on relative). As you are aware, it is mostly ridge walking and fairly level. When you do come to gaps the ascents and descents are fairly short (usually under 500 vertical feet) and have lots of switchbacks. Although the trailway is generally very nice, there are still some rocky sections in the northern half. They are nothing to worry about, but they will give you a short taste of what you would encounter in Northeast PA.
With regards to water, this section is very forgiving. Like many ridgewalks, good springs are sometimes few and far between, but the section has a number of other options that are often quite conveniently spaced. Running water (and often bathrooms with flush toilets) is available at Gathland State Park, MD (Crampton Gap); Dahlgren Backpack Campground, MD (try to plan on spending night here if possible. It has bathrooms, showers and it’s in walking distance to a nice hiker-friendly restaurant); Washington Monument State Park, MD (an odd-ball of a monument that is nothing like the “real” Washington monument); Penn Mar Park (at MD/PA border) and at Old Forge Picnic Ground, PA. You will also cross several streams that could be used for water sources (do yourself a favor and treat any stream water). There are also the usual assortment of springs at shelters, and, with recent heavy rains, they, hopefully, will be running, but, since shelters are often quite far off the trail, you can avoid them unless you are actually staying in them by just filling up at the various parks and streams mentioned above.
Along with the stops mentioned above, make sure to check out each of the overlooks. Most are quite close to the trail and usually the views are quite good. My personal favorite is Weverton Cliffs, which looks down on the Potomac River and Harper’s Ferry, but there are several others that merit checking out, too. Also, if you are a history buff, keep your eyes open for historical markers. The Battle of South Mountain during the American Civil War was fought across several of the gaps in the southern part of Maryland, and the trail literally passes right through scenes of the fighting. Also for history buffs, your stop point (Route 30) is only about 10 miles west of Gettysburg. If you want to see some more history, take a quick cruise through the park before heading home (Route 30 goes right into town and right through the battlefield). It is worth the trouble.
Ken G.