Motor size and Kv advice for ZD550?

There are a lot variables when it comes to building your own drone, so there will be a variety of motor sizes and Kvs that will work.

I think the recommended motor size for the ZD550 is 3508 (like this motor) but that doesn't mean you can't use something different, like a 2814 motor, because a 2814 is fairly similar in stator volume to a 3508. This answer should help you figure out what motors you want. Torque is mostly related to motor size, so you shouldn't have to worry about not having enough torque with either a 3508 or 2814 motor. And these motors should easily be able to carry some extra weight with no problem.

As for Kv, the prop size greatly affects the recommended Kv. Here's a good explanation of Kv and how to choose the correct Kv. The ZD550 frame can fit 10''-15'' propellers, so I would recommend lower Kv (~600) for 15'' and higher Kv (~850) for 10''. Also, Kv will greatly depend on what battery you intend to use. Generally a higher voltage battery = lower Kv motor, and vice versa.