Since I've never played a wind instrument, I'd like to know how to begin practicing with proper technique. The generation of sound for drums lies on the control of the stick (grip, bounce, etc ...); the generation of sound for classical guitar lies on the right hand (angles of attack, length of the nail, etc...) and so on. I imagine breathing and tonguing would be the fundamentals of wind instruments and I want to ask for tips/materials in these 2 areas for a total beginner (but not in music) specifically concerning melodica. For example, I noticed I run out of breath more easily than I would like. I've read several sources that recommend breathing through the mouth and not the nose, which is completely weird to me, since the mouth is already being used to blow the instrument. Also the idea of using the tongue, like spitting a seed, instead of just blowing seems to give me very little difference in sound and less dynamic control.
Yes, breathing and tonguing are effectively the same, though it's not as critical to do them well on melodica.
You breathe through the mouth because you can take a full breath much more quickly than through the nose.
Articulation is important to get a clean start to the note. Simply move your tongue as if you're saying "ta" To illustrate how important this is, try playing a fast string of notes without tonguing ("ha ha ha ha ha" or whatever) vs. tonguing ("ta ta ta ta ta"). I bet the latter is far easier and cleaner.
Try to tongue behind your teeth, not between your lips. Use it to 'kick' the airflow, not to completely bottle it up. And yes, you can get a lot more breath in a lot quicker through the mouth - it's a bigger hole! Nothing weird about using it as a two-way passage.
Unlike a brass instrument where your lips produce the vibration, or a woodwind where your lips touch the reed, you don't have actual contact with the sound generator on a melodica. So it isn't a subtle instrument. But a lot of wind instrument technique is applicable.