I'm going to have to dance around some subjects in case this is being monitored, but here goes.
1) Do not try to evangelize in China. It is a rough calling and illegal, not something you do on the side like you can in Europe or Latin America. Repeat: DO NOT TRY TO EVANGELIZE IN CHINA! Keep your head down and stick to the rules. As an openly Christian foreigner, you will be watched, possibly including bugs in your apt.
2) In a large city like Beijing, there will be an 'international fellowship.' You have to show a non-Chinese passport to enter, so they have the freedom to say just about anything as long as it isn't related to the first point and doesn't speak directly against the government, the party, or communism generally. Go there, just don't take pictures. Some of these people are secretly doing things the government would frown upon.
3) The Three Self Church is the blanket term for all official Chinese Christianity, and is usually more doctrinally sound than the house churches, government oversight or no, and you're not going to be there long enough to build up the 关系(not a good English translation) necessary to meet a house church. Stick to the IF. It's interdenominational, but in the PRC, nobody gives half a crap about denomination.
4) Pray for China. Xi Jinping has become convinced Christianity is a threat to the nation and has been dynamiting 3 self churches, arresting pastors, and visiting towns ahead of charity outreaches to tell the locals all foreigners are to be distrusted. The only thing stopping him from booting all foreigners at this point is a need for investment and teachers (they know most Americans and Koreans wouldn't work in China for what they're paid).
5) Pray for your brothers and sisters in China. New VPN crackdowns may make getting information from anyone other than the government tricky in the next few weeks.
6) If you don't want to follow rule 1, talk to one of your spiritual leaders to see if he can talk you out of it. He may even know people who have been there.