I went on this holiday in April this year. Felt very comfortable wandering around all the cities visited either in small groups or even alone. All the Uzbeks that I met were very friendly and were not trying to constantly make a buck out of you. They were very genuine and pleased to see you in their country. The kids particularly in Samerkand and Shakrisabz were particularly keen to talk to you and have their pictures taken. The best current to take is US dollars but Euros were also accepted in some places. Best rate of exchange was with the local guide who accompanied us throughout. How much you take is purely down to how many extras you wish to buy - drinks in hotels, souvenirs, etc. Only a few meals are not included and they were particularly expensive. The hotel in Khiva is something special. Not luxurious but classically Uzbek and atmospheric.
The Uzbek populations largely speak Uzbek but there is a sizeable Russian population (circa 20%) who naturally speak Russian! Usually someone in the hotels who spoke English but even in the markets the language was not a barrier. The market in Samerkand is by far the best and we visited on the main market day so was bustling in a good way.
This is a trip into a different culture, a unique mix of Muslim and Soviet. Embrace it and enjoy it, I did! It is truly a unique experience.