English will be fine in all three.

I stayed at the Graben in Vienna which was brilliantly located though a bit tired inside. Definitely a good hotel to stay at if you can get a good deal on it - but not worth the rack rate, which I can't remember offhand (I got a flights plus hotel deal from BA). Otherwise anywhere within the Ringstrasse would probably be ok.

In terms of what to do in Vienna, I would pare your expectation in terms of how many museums you want to visit way down. Pick one or two that you especially want to do and spend the rest of the time walking around the city centre and riding on trams. Personally I found the naschmarket a bit of a disappointment, good for cooking ingredients but not for street food.

We stayed at the Imperial in Prague which is a wonderful art-deco place.