I know you were asking mostly about how to get a handle on the electronics and determining what specs a motor has when they aren't given specifically. For you to have the info you need, you will have to be given at least 2 of the 3 primary electrical values.... ie voltage, amperage and/or wattage. If you have two of those, the 3rd value is just a simple math calculation using one of the Ohm's law equations. Resistance is a 4th value as well but very seldom used/given in RC motors. Again, take your time on this subject, it's a big one, most of which you'll learn with experience and not so much reading up on it before you start getting a real handle on it.
What is still the more important aspects of any airplane that you don't want to alter much, no matter if it's a glider, nitro, electric or even rubber band powered... Are where the CG is ( center of gravity ), the wing loading ( how much it all weighs ). The other aspects like wingspan, wing type, angle of attack and other things are more on the engineering side of things if you were designing your own. So pay attention to where the CG is located so you don't change that and keep the total weight down so you don't affect the flying characteristics.
Like on nitro's where they often give a minimum and a maximum recommended engine depending on if you want a slower flyer ( trainer perhaps ) or faster one ( sport or aerobatic )... Electrics often just use a single sized motor that instead use different battery voltages and prop sizes to provide the same effect as the different sized engines. If you do go up ( or down ) in motor weight, as long as it isn't too large of an increase, you can adjust the CG by moving the battery forward or backward. Again, the important part is still to keep the CG in the right place and the weight loading in the range the model was designed for.
Electric motor sizes are measured one of two ways... Most are now measured on the outside of the can. Others may be the size of the stator inside of the can. Going to the drawings are probably the only way to tell most of the time.
As I mentioned... don't focus a lot on learning all about the electrical specs... just know what specs are important and how to calculate what they may not list. Focus more on how much the parts weigh and their sizes. Of course always take into account the quality of a part. As an example, the Eflight Power 25 is a decent motor but Motrolfly's equivalent can deliver more power and is around 30 grams lighter, of course it costs more also.
One last thing to keep in mind... this one is if you plan on converting from a nitro engine over to an electric motor. Nitro engines will use a smaller prop size for a given thrust than what an electric uses. So you'll also have to consider the prop clearance so you don't strike the prop when landing or taking off.
