Your charter company can probably suggest a good itinerary for you. It partly depends on: (1) how much waterline you have; (2) what you want to see/do/experience. If you are interested in locations where this is a lot of human activity/nightlife, then sticking to the western shore (Baltimore/Annapolis) will suffice. I agree with the earlier post that Solomons Island is a bit of a stretch for a 4 day trip (unless you have a lot of waterline and a fair breeze).
But if you are more interested in the bucolic settings of the Chesapeake Bay, then head to the Eastern Shore. Two possible itineraries: (1) Annapolis - Wye River (via Eastern Bay) - St. Michael's - Tilghman Creek - Annapolis (Via Eastern Bay); (2) Annapolis - Dunn Cove (on Harris Creek, via Knapps Narrows) - Oxford - La Trappe Creek - Annapolis (via Knapps Narrows). Either of these will give you a good mix of quiet coves and interesting towns with provisioning/restaurants.
As for swimming, July will be a bit iffy. The water will be plenty warm, sure, but the jelly fish (what locals call "nettles") could be thick by then. They are not lethal, and many of us risk their tentacles for a swim, but they can be VERY uncomfortable if you have a brush with them (make sure you have vinegar aboard to neutralize the venom). On the two itineraries I suggested above, good swimming can be had in Wye River, Tilghman Creek, Dunn Cove, and La Trappe Creek. Have fun!
P.S. Thunderstorms can be a real menace this time of year. Keep a weather eye (most approach from the west during mid-late-afternoon) and be prepared to drop sails if one approaches. You can usually see them coming a long way off, so don't worry, but they can be fast moving and pack a punch so don't be complacent either.