One thing to keep in mind with an ESC is that its current limit is primarily determined by its ability to dissipate heat. So if you put an ESC inside a foam fuselage, its effective rating is going to be much lower; and if you put the ESC on the top of the plane, exposed to airflow, its effective rating may be higher. But honestly, manufacturers are probably generous when they spec their ESC's, which is why you should add 20% or so, and if possible, get the ESC into the airflow for better cooling.
Choosing a motor and prop is a pretty deep hole to get yourself into. Here are my thoughts on it.
You have two main constraints to start with. The first is that your plane probably can physically only take so big of a prop. The second is that you need enough power to make your plane fly--the wattage requirements you list. So let's say that we decide that our plane needs around 300 watts of power, and it can take up to a 10" prop.
Now you go look for motors that run on your desired battery voltage (3S? 4S?) and make 300 watts of power. Any motor that you can't find published thrust data for, in my opinion, just pass on it. It's just a crap shoot, unless somebody tells you that they have the same frame and they know it works.
Motor weight. Motor weight is going to affect your CG, so the motor can't be too heavy. But there is more or less a direct relationship between a motor's power rating and its weight. A rule of thumb is 3 watts per gram. So if you need 300 watts, you're looking at roughly a 100 gram motor, and if your CG won't tolerate that, you have to re-examine some of your assumptions.
What prop do you want to put on your motor, and what kv motor do you want? If you need to spend 300 watts, there are various ways to do that. You can spin a small prop really fast (high kv) or you can spin a big prop slower (low kv). Bigger props spinning slower are more efficient, so if flight time is your goal, you want to get the biggest prop and the lowest kv motor you can fit on the plane. But a plane's speed is determined by the pitch of the prop times the prop's rpm, so if you want a plane to go fast, you may want a smaller prop being pushed by a higher kv motor.
The other part of the equation is thrust. Thrust is what makes a plane accelerate quickly. A plane with low thrust and a high top speed will be like a car that only has a high gear. If you push the gas, it will accelerate slowly. Eventually, it will get going very fast, but it will take forever to get there. Thrust is also important when climbing. The more thrust you have, the faster you can climb. Thrust is primarily determined by the size of the prop.
So, to sum up: bigger props make more thrust; higher pitch makes a plane faster. As you might expect, making more thrust and making a plane go faster takes more power. So you can think of your power budget (300 watts, or whatever) as being divided up between thrust and speed. You can have a plane with lots of thrust and low speed (like a big prop with low pitch--a 10x4.7, for example) or you can have a plane with little thrust and high speed (a 6x6 or a 7x7 prop). Or something in between. But as long as your overall power budget is fixed, you will find there is only so much thrust and speed you can get.
How much thrust do you need? The absolute minimum is a thrust-to-weight ratio of about 0.5:1. A TWR of about 0.75:1 will be less on the edge. A TWR of 1:1 is starting to get pretty acrobatic, and will be able to go vertical, but not unlimited vertical. A TWR of about 1.5:1 or higher is getting into 3D and unlimited vertical territory.
So let's say your plane weighs 900 grams (I'm pulling these numbers from my own personal experience) and you have a power budget of about 300 watts. A power budget of about 300 watts will give about 150 watts per pound, which makes this plane pretty powerful. And I want good thrust performance, so I'm looking for about 1200 grams of thrust, minimum, and 1400 would be better.
So let's look at some motors. Maybe first I decide to check out the motors I'm using on my quad, which is the SunnySky 2212 kv980.
Here is a link to some data for that motor.
The first thing I see is that the motor weighs 58 grams. Our rule of thumb of 3 watts per gram tells us this motor should handle about 174 watts, so already things aren't looking good. If we look at the thrust data, we see that the motor generates 910 grams of thrust at 14.5 amps. This is a TWR of barely 1:1, so it's not what we're looking for, for this plane. Also, our plane can't handle an 11" prop. Whoops. On a 10x6 prop, the motor generates 731 grams of thrust drawing 10.45 amps. This is a TWR of about 0.81:1. This would be fine for a trainer, and it will be fantastic for battery life, but it's less thrust than we want.
Well, what if we went up to a higher kv motor? This would spin the prop faster, and generate more thrust. Here's a link to the 2212 kv1400. This is the same class of motor as the 980 we looked at, just higher kv.
Here is a link to its test data.
This motor can only handle up to a 9x5 prop, so it fits our size requirements. It generates 1015 grams of thrust, drawing 18.9 amps / 200 watts. This gets us into the 1:1 TWR range, and might start being acceptable. Notice that this motor weighs 58 grams, but it handles 200 watts, which violates our 3-watts-per-gram rule, which is why that is only a rule of thumb, not an absolute.
We are looking for a motor in the 300 watts range, but it looks like the 2212 motors may be a bit small for our purposes, so let's go up to the next larger motor in the line, the 2216. Perusing the 2216 line, we see that the 1250kv motor (
specs here) makes 1136 grams of thrust drawing 21.7 amps / 227 watts. It weighs 72 grams. Now we're starting to get somewhere. The person running the test also tried a 10x6 prop, which made 1400 grams of thrust, but he said in the review that the motor got too hot and he wouldn't recommend using that prop. Boy, if we could use that prop, that motor would be sweet.
It is starting to look like the 2216 line may be about the right size for our purposes, but the thrust made by the 1250kv motor is still a little less than our desired TWR. 1100/900 = TWR of 1.2:1. Not bad. This is probably the smallest motor we would want to use. One thing to keep in mind is that we are drawing 21.7 amps to make 1136 grams of thrust. We can get a motor that will make more thrust, but unless we can go to a bigger prop, we are also going to draw more current. So in order to get to 1400 grams of thrust, we might need to pull closer to 30 amps, which will cut down our flight time substantially. So there is a balancing act there. If you are willing to pull 60 amps, you can get a hoss motor that will spin a prop super fast and blow your doors off. But you'll need a huge battery to feed it.
The next step would be to look up what the next-highest kv motor in the 2216 line is, and see what its test results are. What you'll find is that the higher kv the motor, the smaller the props will get, in order to keep overall current below what the motor will handle. At a certain point, if you want to use a prop of a certain size (10", for example) you will not be able to go over a certain kv without going to the next bigger size of motor.
Anyway, hope this gave some insight...
