I’ve posted on this before (and been flamed for it) that I climbed the Matterhorn with a guide, and thought it was an awesome experience! So here are my thoughts:
First off, it sounds like you won’t have any problems technically with the difficulty. It’s rarely anything over 5.4. The cardio and endurance is the hard part. I was going nearly all out for 3 hrs, 40 minutes from the hut to the summit - one 10-minute rest break. While the guides will turn you around if they think you are too slow, I saw few guides turning their clients around. The ones that were turning around were exceptionally slow. My guide expected us to summit in 4 hours or less. In retrospect, a good thing, as the beautiful summer day on the mountain started to totally sock in as we reached the hut again. And we descended in just over 2 hours. As for a guide dragging a cow up there, it’s likely that they could (they’re good at what they do), but none that I met in 10 days climbing around Zermatt would. They expect you to be ready for it.
As for your questions:
Get a guide at the Zermatt office (I can give you a name). They know that route inside and out, improving safety and speed. They guide as an “aspirant” (trainee) for 2 summers before they are allowed to do it alone. I met a fair number of the guides, and found all to be friendly and genuine. I met some of their families, and was told to come visit anytime.
If you go the last half of August you’ll have less people on the route (prime season ends around the 15th), but the weather will be more hit-or-miss. I did it on Aug. 2nd or 3rd, and even then it wasn’t too crowded in the hut or on the route.
They do most definitely short-rope. It was my first experience with it (first experience with a guide, actually), but not at all worrisome. Yes, if they fell it could be bad, but they are good. They do running belays in certain places, and belay off fixed anchors in the toughest spots. It most definitely has places where a bad step could be disaster (take one big step out the door of the Hornli Hut), but I felt secure. The alternative is setting up numerous belays, making a 6 hour round trip into a climb that can possibly take 2 days. I thought it was well worth the slight perceived risk.
So, those are my thoughts. Hope it helps! Let us know if you have other questions!