We recommend to get the Visa support letter from the hotel. Such letters are usually provided by the hotel after booking a room. This service is free in some hotels and paid in others (about $ 25). The beginning of summer is the high touristic season in St. Petersburg, so we recommend you to book a hotel room as soon as possible.
It is better to choose hotels located within the walking distance from the University.
The distance from these hotels to the University is about 15 minutes walk.
Hotel "Saint Petersburg" is located a little farther (about 40 minutes walk).