Mark, I didn't mean to slam you for asking the questions, just trying to point you in a direction where you will learn what you need to know.
If your question was primarily about the issue of finish penetration... that is an interesting issue and one to pay some attention to. Finishes are often described as being either film finishes or penetrating finishes. As I see it, it's a bit of a false distinction. A lot of it just has to do with viscosity -- any finish that's runny enough, i.e. thinned with enough solvent, will penetrate. Pure oil finishes will tend to penetrate more even at thicker viscosities, if you flood the surface and let it sit on there a while before wiping it off. But even oil finishes, if they're "finishes" at all, i.e. oils that will cure, form a film on the surface.
You don't want a finish to penetrate very much on a guitar. So if you use a wipe-on finish that penetrates a lot, you want to wipe it off quickly so very little soaks in, then let that coat cure. You've now got a very thin film on the surface. Each succeeding coat will penetrate less because the surface is more and more sealed with the film you're building.
A bit of penetration can be a good thing. E.g. with an oil finish, that's part of how it pops the grain nicely and looks the way it does.
You can also reduce penetration of any finish by wiping on some shellac first. This will give a different look, but it can be an effective technique. Shellac goes on as thin as water, but because you don't flood the surface with it, and because the alcohol evaporates almost instantly, it doesn't tend to penetrate very much. And it seals the wood well.
A gel hardly penetrates at all, just because it is so viscous. I haven't used the Minwax wipe-on poly, but I doubt that over-penetration would be a concern with it. If it seems to be a potential problem, you would just want to wipe it off quickly. Or, you could seal with shellac first. Shellac first on the bare wood might give you a nicer look - better color and better popping of grain. I found that to be very true with the McFadden's gel. Putting that stuff on bare rosewood didn't look good at all. Over a little bit of build of shellac, it looked great.
I hope this is helpful. I don't think you're making it "more complicated than it needs to be". The chemistry and behavior of finishes IS fairly complicated. But not so much that you can't get a grasp on a lot of it pretty quickly if you're hungry to learn and get some good books. Flexner's book, while not the last word on finishes, will give you a lot of very useful information and de-mystify the subject.
Good luck!
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