I've taken eight RS tours as a solo traveller, and every one of them was fantastic. As others have mentioned, paying extra for the single supplement is a good idea. If there are more than one single of the same gender on your tour, you'll be rotated through different room mates. Some may be easy to get along with, but others may not which would make for a miserable time.
There are pros & cons with both the fully guided and the May Way tours. With the My Way you'll have to do more work to figure out your sightseeing as that won't be covered, and admissions to any sights you want to see won't be covered. You'll probably learn more on the fully guided tours, as the local guides cover a lot of interesting history. The group meals on the fully guided are awesome, and tour members dine well.
"It was very isolating to not know anybody, not know the native language, and not have anyone to hang out with or just compare notes with. My whole trip I largely only communicated with waiters, shopkeepers, and the guy at the hotel desk! The other tough thing was trying to arrange various side trips, transportation etc. and dealing with outdated schedules / incorrect information / pay phones that didn't work / cell phone not working etc."
I often travel solo and have experienced much the same thing. Those are just some of the differences of solo travel, and I don't usually find things like that to be a problem. Solo travellers often tend to me more outgoing and more approachable by other people, as opposed to couples. I always seem to find people to chat with, other than waiters or shop keepers (often other tourists - I sometimes get some good tips by comparing notes).
My side trips and transportation are usually very well planned, so don't often have a problem there. Language has not been a huge issue for the most part. I always try to learn the usual "polite words" for countries that I'm visiting, and have found that most people in the tourist industry can usually speak some English. However, every so often I encounter a "challenging" situation (that was the case in Poland last year), but with some help with a phrase book and a few hand gestures, I can usually manage to communicate. Whoever said that most of the younger crowd can speak English doesn't know what they're talking about! My cell phone has always been very reliable, although I did have a few "connectivity issues" in Croatia last year.
The biggest issue that I've found with solo travel is not having anyone to share my wonderful travel experiences with. I can enthusiastically relate the details of my trip to family and friends, but usually just get a cursory, "oh that's nice" or "it sounds like you had a great trip", as their eyes glaze over and they start looking at their watch. I guess that's one of those "you had to be there" situations.
I'm sure you'd have a great time on that tour!