I'm 6'2, 250 pounds, and I've done 4,000 miles on my 2010 C5, including three round-trips between NYC and DC with large saddlebags thrown over the back. The riding position is comfortable (better than my other bike, a Honda CB250), although on the long trips I do stop every 30-45 minutes or so to stand up and stretch my legs.
The bike does fine on the highway. It can cruise at 65-70, although there's not a ton of passing pickup beyond that. It's not the fastest bike on the road, but that's not why you bought it. You'll want a windshield if you do a lot of highway.
It's a quirky bike, which means that if you run into trouble on the road, it might be hard to find a mechanic who can help you. When I was new, I had to truck the bike back from Annapolis to NYC in a U-Haul when I had a mechanical problem on the road because no shop would touch it. When I got home I figured out that the problem was simple and if I had known the bike better I could have fixed it on the side of the road in 30 seconds. (In fact, that's what I did when i got home, on the side of the street in Brooklyn, with this forum open on my laptop on the bike seat.)
So I guess what I'm saying is that it's the kind of bike that will reward getting to know it. I've learned more about vehicle mechanics in the last 6 months than I learned in the previous 40 years, but that's not a complaint -- I knew going in that I was buying a piece of history. No problems whatsoever with the engine -- the new UCE engine is a well-made piece of machinery and it starts and runs perfectly every time.
If I were buying from Baltimore, I'd probably see if I could buy from Philadelphia Scooters, so I had a relationship with them in case something goes wrong. They're an authorized dealer. (Yeah, I know, 100 miles away. What are you gonna do.) I did have a transmission problem on my bike that was covered by warranty (you can read about it elsewhere on this forum), and I had bought from a non-official dealer, and until I got referred into an official dealer by CMW (Classic Motorworks, the US RE distributor, and the host for this forum), I felt a little lost. Once I did get a referral (to a dealer about 50 miles from here, which is one of the closest), they were able to address my issue and I now have a good dealer relationship I can call on in the future. I have no complaints about CMW -- Kevin from CMW participates actively in this forum, they respond to us, and they really know their bikes well.
Short version: Do it, you'll be glad you did.