You might not have a method yet to share on abbreviations, peggyjo, but I sure have noticed you have a lot to share here!
I'll answer your questions as *I* see them - doesn't mean it will be right for you.
Yes, these are Grow method shorts. They mostly work for me for
three-word phrases. That is when they seem completely awesome and natural for me. They do not come naturally for long sentences or phrases and thus I do not use them for that. Now, I'm not saying I don't use it at all for any four or five word phrases, but somehow, for me, it's the three-word phrases I mostly use them with. As you pointed out yourself, a lot of three-word phrases are just naturally going to end up with duplicates or even just lots of "close" ones, and while I look at my advisories all the time (back and forth, that is), for continuations and to be sure I pick the right entry for phrases, nothing, I mean NOTHING, is better to me than knowing instantly what the entry is and go with it, never having to move your eyes. That's why I'm a system lover, and that's why these work for me. But yes, there's tons of situations where this method is not for me. I like the ABCZ method for two-word phrases and many single word examples, for instance. And then, I have the mix from just starting out a certain way. Also, lest I mislead you, I do have many, many three-word phrases that I simply use each first letter of the phrase for, so it isn't like I do this for all of them.
I love IT standard shorts for longer phrases. I add letters to the beginning or end of the short on occasion to what IT has put, but probably the majority of the time not. And it's so nice that IT fills in the short for you. I love that.
The one thing I don't like to do, is have words in the word section, with a one-letter abbreviation. (I don't mean the singles here). It's a feature and lots of people like it; but I just don't. Which isn't a problem because I don't do it, ha! IT is about nothing if not choices, lots of choices.

As I said, I don't like to look off the screen when I don't have to. It makes me feel more prone to blooper mistakes and it also takes time; sure just a second or two, but time nonetheless. I love the ABCZ system for words and also I have made up lots of "odd" shorts for words. Of course, phrases is where the action is at overall.
I think you should take note of all the systems out there right now and play with them, and play with IT, but I definitely don't think you need to "decide" on anything in a rigid manner right now, and also I just think you should just go with the flow, so to speak, because when you start working it will all "hit" you and you'll come to know very soon what works best for you.
You do have to sort of train yourself, I suppose. But it isn't hard and to me it's very, very worth it.
All I can say is, even for an MT who has never heard of any systems, never thought about them, isn't even an "internet" person, you will end up making adjustments for duplicates and entries that might be a poor choice. But not to a degree that I want to have. Well, let me change that to say that "I" didn't have my entries set up in a really, really good manner for a long time. And then when I ordered Jon's ABCZ files for Shorthand, which is what I used at that time - wow, the light freakin' went OFF! I could see the difference! Took me a little bit of time to adjust to the system, of course, but wow, did I ever see a jump in productivity. And ever since then, I've been more and more interested in refining techniques. And yet at the same time, I've become very appreciative of IT and the fact that this doesn't "have" to be. Very paradoxical, eh?? LOL.
Take what you want from the different systems out there and leave the parts that don't work for you, that's all I can really say. And make up stuff! Even crazy stuff! Those entries are also wonderful!