How much have you guys made in the gaming niche? and how?

Well, streaming has really come a long way since the exceeding progress of GPUs and CPUs continues to grow.
If you're going to be a PC gamer, you're going to want to invest a good $300-$400 USD into a decently running build - as well as make sure that your internet speeds (mainly upload for streaming purposes) are up-to-date and in compliance with optimal streaming performance standards.

However, you may go with the mobile gaming aspect and do it all from your device (gameplay, stream itself, etc) but this would require you to have a higher-end device, such as the Galaxy S8, S8+, S9, S9+ for Android (or the OneTouch brand) and anything above the iPhone 7 for Apple.