I always include options for ballet, opera, folk-show or concerts when finalizing the program. The reason that I can't do it earlier is that St.Petersburg's theaters announce their programs relatively late - only about 2 weeks in advance, which is why it is not worthwhile looking for details any earlier.
Please consider that the internet is not the best source of information about cultural events in St.Petersburg. Only the most promoted Mariinsky (Kirov) theater and folk-show at Nikolaevsky palace have decent Internet sites, while in reality during summer you have a much wider choice of about 4-5 ballet or opera performances daily, plus occasional concerts. The choice between September and May is even better.
Being your guide I will help you to choose the best option for the days you will be in St. Petersburg and buy tickets in advance for you.
Lunches and dinners
I do not always specify dinners on the programs. This does not mean I will leave you exhausted in the evening to look for a restaurant on your own. Usually I leave my guests only once I am sure that they no longer need me i.e. I would not take you back to the hotel before you had your dinner after the sight-seeing day. I don't specify it on the program mainly because we usually decide such things at the last minute - e.g. what kind of restaurant do you fancy tonight? Being Russian I believe that a program where everything is decided upfront leaves no space for imagination.
Dates and length of the tour
It is you who decides when and for how long to come. However, if you are undecided between two options or are flexible about dates / period of stay, then I will be happy to help you give you my advice.