I found this great video that talk about the process for choosing the best motors, props and ESC for your quadcopter. It is a great process you should follow when you are building a new multicopter. The video focuses on quadcopters, but the rules are the same for Tricopters, Hexacopter, Octacopters etc..
Some Side Notes
- When he is talking about the thrust required for your motors
(model weight x 2.2)/no. motors you should try look for motors that have the max thrust values that match that weight. However he talks about motor efficiencies dropping down at higher throttle, but this is usually included in the values provided by the manufacturers, as the thrust tables are usually given at max thrust. I would also speculate if you are not doing aggressive flying you can comfortably fly with a hover at 75% throttle. This gives you some extra weight you can use for a bigger battery.
- In terms of ESC suggestions having 20% extra Amps is a good rule of thumb to ensure your ESC dont burn out, but its also good to remember that if you are doing conservative flights then you will hardly fly at max throttle, and most ESC have a burst Amp rating that they can sustain for 10-30sec. But he did suggest that if you are undecided about two ESC ratings, always go to the higher value, this is again a good idea, but if you are using a larger ESC can also use more battery , so its something to think about.
- If you are wounding about how big your battery should be, in general you should choose a battery that is as big as possible! Most of the quadcopters that can fly for decent times have a battery capacity that consists of over 50% of the total quadcopter weight.
Hope that helps, and if you have any of your own pointers or questions let me know!