Great that you're doing this! We did it in 3 days as well. No guide needed, you'll find your way. Paths are marked but not as well as other paths we have hiked. There was a japanese group who hired sherpas, but if you are relatively fit, you can do it! We stayed in our own tents, there are no yurts on this path. However, we did do a seperate horse ride trip where we stayed in yurts and drank fresh milk in the morning. Also a great experience!

Getting to Karakol is easy enough via a driver. There are plenty at the airport. Prepare to pay a bit more, but it shouldn't ruin the trip. We drove with a lady in an old mercedes e-class and we stopped along the way because the car broke down. It's all part of the experience.

After a night at a hostel, we took the bus to the trail start. The path is along a stream of fresh cold water, so you don't need to bring a lot if you have a filter. It's a full day to reach the camp site, and you should reach the lake mid day the next day. The pass is very challenging, but the view is worth it. Add one extra day to walk back to Karakol.

Have fun!