Welcome aboard the RoadTrip America Forums!
And welcome to the world of RoadTripping, where the primary tenet is that the 'best' RoadTrip is whatever you decide for yourself. What you'll find here are some suggestions, but no hard and fast rules or 'must-see' attractions. That said...
Let's deal with destination first. There are a couple of factors to take into consideration. First thing to take into account is the time you all have available. That will place constraints on how far you can get before you have to turn back. As a rough rule of thumb, you can multiply 150-200 miles times the number of days available to give you an absolute outer limit on how far you can get before you have to turn around. Thus for every week of your RoadTrip you can plan on getting about 1500 miles (at most) down the road. Remember, that leaves time seeing things on the way and at your final destination as well as getting back home. If anything, err on the short side of that estimate.
Another constraint is money. Currently gas is around $2.80/gal nationally, a little lower in some areas, a little more in others. So, budget for about $3.00/gal. How far that gets you or how much money you'll need for gas depends, of course, on which vehicle you end up using, how far you end up going, how many side trips you make, etc. You can use the RTA Fuel Cost Calculator once you have those details worked out, but for a quick reference and using rough figures a trip to the Grand Canyon and back in a moderately fuel-efficient car should cost you around $750 - just in gas!
The next major cost is food and lodging. You say you'll handle these independently, but in fact they are much better done as a group. For example it simply won't work for one of you to plan on staying at the nearest Hilton and eating at four-star restaurants while another expects to camp and roast hot dogs. Those are just a few of the travel-style details that you all need to work out now, before your trip. Again, as a very rough rule-of-thumb, you should plan on around $75/day/person for food and lodging at very modest establishments.
For some more unforeseen problems that might come up when traveling with friends/strangers, check out the Compatibility Quiz. Which brings up one more object of consideration in your planning. Be sure to schedule 'time-outs' during your trip. However strong your friendships, they are going to be hard pressed to endure even a couple of weeks of 24/7 togetherness. So build ways to get away from each other into your trip, such as a couple of motel rooms each night and switch out who shares a room with whom; days where you each simply go off on your own in a city or at a major attraction and then compare notes at night; certainly days where you are not just spending eight solid hours cooped up together in the car.
Finally (yes - finally), comes the choice of where to go. With an idea of how far your available time and money will take you, and an idea of what you all want out of the trip, sit down with your friends and a good road atlas and take a look at what's available within that range. Since you'll be traveling in summer, there should be no weather restrictions so almost anywhere within range is a possibility. Look not only at your end destination but especially at what's between Cumberland and that destination since it's 'in between' where you'll be spending most of your time. It was my privilege, when I attended high school outside Baltimore many years ago, to have several classmates from Cumberland and Frostburg. The phrase I later learned (when I lived in Maine) to describe them was "Finest Kind". I wish you and your friends all the best.
AZBuck