I plan to go to Harbin. Some questions arise in my mind, as follows: are there any Moslem food there

Beijing is a good city to start with. There is no big difference between airline companies, just compare and choose one suitable to your departure time or select the cheap one.
There are muslim restaurants and food in the city.
What kind of hotel do you prefer? When traveling in China, I usually use the chain economical hotel, such as seven days inn, home inn. They are cheap and there are many branches. You can easily find one in your prefered staying area.