I went on this tour in July 2012. It was amazing! I also stayed at the Hotel Sumengen, which is only a 5 minute walk to the Blue Mosque and Hagia Sophia ( I will admit- kind of hard to find for my taxi driver - there is a small bazaar next to the two mosques called "Arasta Bazaar". Down the hill, about a 1 minute walk behind the bazaar is the hotel).
About the tour itself - there were two VERY heavy duty walking days in a row with this tour, near the beginning of the week. More so than on the other 3 RS tours I've taken. It's not hard walking, but long. It will help that you're going on March, not July though, so that's good. You do have some free time later in the week to do whatever you want. I'd like to go back and spend more time on the Asian side, which I only got to on the day we had a group dinner over there. You may want to check it out too - less tourists (again, going in March will help with that anyway I assume).
The sites were really cool! Our guide was Yaren, who works for a company that contracts with RS. She was awesome! VERY knowledgeable and very friendly!! Make sure to spend some time on Istiklal Caddesi ( a pedestrian street with shopping/restaurants, etc). I'm pretty sure that the tour goes here, but I went separately with a Turkish friend too. Down at the far end is the hotel (forget the name) and train station where the Orient Express would originate. I didn't get time, but some tourmates went to the Hotel for tea and had a great time.
Have fun! Istanbul is HUGE, but lots of fun!!!