請問四月上旬是否適合到東歐旅遊?

I have visited Hungury and Romania just in early June last year... Which is just two months later than you... The weather was really good... Sunny mild dry weather... And the weather could get up to as hot as 40 degrees... But you wont feel it as it is rather dry...
But in March/April, it should be the best time to visit Eastern Europe... As the weather just begin to change from a colder winter of around 10~15 degrees to the summer 35~40degrees... So the weather at that time in Eastern Europe should be around 20~30degrees... Not too hot but not cold... There are very little rain as well in Eastern Europe so you should see a pretty sunny mild dry weather through out your stay... Maybe a day or two rain but not a lot...
Hope these information will help you... And have a good trip to Eastern Europe...
But you may find that majority of the buildings at all those 3 countries would be in a very similar style... Out of which, Czech Rep and Hungury could be rather different than Austria... As Czech Rep and Hungury would have a mixture of classic building and also the side of poorier Europe and less advance compare to place like Austria...

take care of the gipsey too~
enjoy ur trip~