Hi! I had the same questions, but nobody answer them so here I am to answer for next travellers, when arriving at Tashkent airport, there was only one ATM that was giving US DOLLARS, there was no booth to exchange money at the arrivals, I had to go up one floor to the departures to exchange money, I exchange 50$ Us and they gave me 120000 soms, I though it was a good rate but later to find out that on the street the money changers would give me 155000 soms, so therefore don't exchange too much money at the airport.
As for a taxi from airport,I walked out of the main area where licence taxi wait and went to the right of airport and there was plenty of them wanting to exchange money, I bargain a taxi for 5000 som to get me from airport to bus station it's about 15 min ride, they will ask crazy prices 50$, 25, but stick to the 5000, the price is good as I had ask a police man In the airport.
When I got to the bus station, I wanted a share taxi to go to Samarkand, there was like 50 guys waiting for me and yelling and grabbing me to get me in the taxi, then again they were asking crazy prices, I knew it was between 30000 to 40000 som, it was so crazy I just took the first guy who agreed for 40000 and jumped into his cab, it was crazy be prepare. Taxi 3:30 hrs to Samarkand.