Visiting Vienna is a great idea and you will be able to see lots of interesting things there. So if you are 100 % sure that you want to go there start planning everything early in order to have a chance to see everything worthy. Start sightseeing and you will see that you won’t have enough time to pay attention to everything.
By the way if you are interested in vegetarian restaurants you don’t have to worry. The city offers a big variety of restaurants and everyone can find whatever he wants. I would recommend you to try some of the local cuisine because it is certainly great but since you are interested in veggie restaurants I can give you some tips as well. I have a friend of mine who lives in Vienna and is really fond of vegetarian restaurants. He knows all of them.
As a beginning you may take a look at this link http://www.lonelyplanet.com/austria/restaurants/vegetarian – it will give you a good start, plus you will be able to read lots of reviews and opinions about the restaurants. In that way you will be able to find the best place that suites your expectations. Anyway if you don’t like anything interesting in this site or nothing that can convince you to visit a certain restaurant you can always try this one as well http://www.happycow.net/europe/austria/vienna/ Like the first link here you can find lots of restaurants and people’s opinion. It is always recommended to get a look through sites like these because you can find some really valuable information and as you know it might be quite hard to find a decent restaurant in a place you have never been before. Believe it or not but if you don’t enjoy the meal in a certain restaurant, then you’d think that all of them are the same and the city will make a bad impression on you. This is why it is so important to read some reviews. Basically the site of HappyCow covers the entire world so you may find vegetarian restaurants wherever you want.
Last but not least I want to say a few words about the accommodation. Finding an Apartment Vienna is much easier than finding Milan apartment or apartments Poznan and this is why I would recommend you to rent an apartment rather than stay in a hotel. It is more spacious and often the prices are lower. This is why you should pay attention to this advice. If you make a search on internet you will find thousands of offers. Plus you will be able to filter the price range and other information. Just make sure you are in a decent neighborhood. If you can, rent an apartment in the center because in that way you will be really near to all of the important things and restaurants in the city. After all, this is why you went to Vienna – sightseeing and going to nice vegetarian restaurants.