1

I spent about that amount of time in Uzbekistan in 2008. Not too rushed and saw plenty.
I went Nukus-Khiva-Bukhara by bus and taxis then Bukhara-Samarkand-Tashkent by train.
(I could have added one or two places more but I was having problems getting visas sorted for my next stages)

2

It is plenty of time depending on your itenery. The Fergana Valley is large and some of the towns are not worth the travel, however Kokand is very interesting (an old Khanate). Termiz is rather isolated, and Tashkent, Samarqand, Bukhora, Khiva, Nukus (Arial Sea), are spread out so you cannot go from one to another quickly. Give yourself some extra time. I used to work there, and I joked that the locals would say "meet you at 2PM", BUT they did not say which day of the week. Time means much less to the Uzbeks, and you have to deal with it. March may be warm, hot, cool, cold, dry, wet, raining, hard to say at this time of year. You will be there for Navruze March 21, a big drunk celebration. Watch your valuables, there are lots of light fingered folks there.

3

3 weeks is a good amount of time. If you factor in the long drives between say Khiva and Bukhara and you'll want to schedule more days in the cities and not travel every second day.

4

Ideas about a 3 week itinerary in March maximizing outdoorsy stuff?

5

Well on your way back from Samarkand to Tashkent (or vice versa) the Zaamin National Park is a must if you want to get some outdoor experience. Camping or staying in a guest house is possible. I would also suggest going to the Aydarkul lake, which is 100 north of the town of Nurata. There is a yurt camp there and you can ride a camel. Take a shared taxi from either Bukhara or Samarkand to get there through Nurata (there are also some historic sites to see).

6

Thanks Vldash, are these good for hiking in March?
-TBri