If you’ve decided that you’ll shoot with two cameras, here are the three things to worry about.
Make sure audio is being recorded separately and slating is done for both cameras for syncing in post.
If possible, try to make sure that you’re using the same camera. In the world of DSLR filmmaking, the sensors of the different cameras can be significantly different on how they capture light. This will produce different color schemes and graininess for the same lighting conditions. If you don’t have a choice, this is not the end of the world, as color correction in post is always available. But if you haven’t engaged in that kind of post production, it might be a good idea to find someone with the same camera as yours for your multi-cam shoot.
Lenses are the other issue. If you’re shooting opposite sides of a conversation for instance, it would be ideal if both sides looked similar, and that can be achieved with lenses that are similar, with cameras that are equidistant from the subjects on either side. Anything else might look a bit off. And one of the goals for us filmmakers at least at this beginning stage should be to make sure that our cinematography is not distracting to the point where the audience is thinking about it. The audience should only be thinking about the story, not about why one actor appears closer to the camera than the other.
So, ideally try to make sure the second camera is the same as the first, and you have a similar set of lenses for each camera. It’s easy to say this I know, but beg and borrow to make sure such is the case for your shoot. Otherwise you’ll be spending a lot more time in post production than you’d care to.