I, speaking as an expert, highly recommend not taking the approach you are taking. I also speak as one in my 40s (43)
Thanks, ThrillerFan, for your detailed honest answer (and BobbyTalparov for the second). I will say this... as much as I talk and argue about openings, I hardly look at them and so I really don't know what style I would prefer. Really, I will play anything that I think has well-written and fairly comprehensive resources and isn't insanely dubious.
I have looked at the KIA/KID/Pirc because that comes up often when one searches for universal openings... many players have advised against it for me (well, against the KID/Pirc, not so much the KIA), saying the positions are too complicated and, as Black, a lower-level player will be in the uncomfortable position of having a lot less space.
The narrow repertoire I posted was a suggestion by a master a while back who knew my schedule limitations, but was struggling to figure out what may be better for adults with other obligations. the gist of what he suggested was...
Wedge patterns are easier to learn, hence the London as White, the Scandinavian (he suggested 3...Qa5) is "simpler" than the Caro-Kann, and the Baltic is a reverse London, not so great, but certainly fine through the higher club level players. But "ideally", he wanted me to go the route of Ruy Lopez as White, 1.e4 e5 and Nimzo against 1.d4 as Black, etc, to get exposure to "a variety of pawn structures and strategic plans."
But you should know what type of central structure you prefer.
Forget about openings. Pretend they don't exist and never did. When you play chess, what type of center do you feel the most comfortable playing? We are talking in the middlegame here! Do you do best when the center is completely blocked and all play is on the wings? (I raise my hand to that one). Do you do better when the center is wide open and piece play along with being ahead in development and able to find deep tactics is critical? Unlike blocked positions, neither side has the time to maneuver knights around from one side of the board to the other. Do you prefer positions that are not completely blocked, but maybe a pair of central pawns are blocked, like in the Queen's Gambit, where the d-pawns can't move, but there are pawn breaks on the c-file and e-file?
That's how you need to approach it. Determine they type of middle game that works best for you. Only after you have determined that do you start looking at which openings lead to it.
As mentioned before:
The French and King's Indian lead to a completely blocked center.
The Grunfeld and Alekhine lead to a mobile pawn center, where White controls the center, and Black attempts to break it up before White is able to stablize the space advantage or advance the pawns to the point that stopping them is a liability.
The Petroff and Tarrasch lead to very open positions and often involving an IQP, so knowing how to play with the IQP (Tarrasch) or against it (Petroff) would be vital.
The QGD and Closed Ruy Lopez lead to what is known as the Static Center, where again, there is usually one set of blocked pawns (d-pawns in QGD, e-pawns in Closed Ruy Lopez) and neighboring pawns are often breaks.
But choosing the opening and then learning the pawn structure is the backwards and wrong way to do it. Figure out your middlegame strengths first. Which positions are you winning and which are you losing? Then determine the opening appropriate for the situation. And many on here are going to simply suggest what they play themselves. You are not them! I mentioned that I advocate the French and King's Indian, but if you don't do well in blocked positions, I am not going to lie to you and say the French and King's Indian would be recommended in your case just because I play them, but if you do prefer blocked positions, then by all means, there is your answer!
Think of it like basketball. A good coach uses the player's strengths. A bad coach or owner (cough - Phil Jackson and his STUPID Triangle Offense that Carmelo Anthony couldn't do jack with) will force feed his system. It would be the same as me telling everyone that ever asked me a question about defending e4 that the French is the ultimate answer for all of them! It's not!
All I can say is how one should decide their openings, not force feed them to play them. I can walk a horse to water, but I can't make him drink it!
"One particular approach to opening repertoire management is the use of universal systems, ... The use of such systems can enable a player to reduce the amount of opening theory he needs to study, and to reach positions of a type he is familiar with and enjoys playing. It is to the pros and cons of this approach that we now turn. ... it is rather more difficult for Black to adopt a universal system, ... The most popular one ... I will discuss in the next section. ... I refer to the King's Indian/Pirc/Modern complex. These lines are characterized by a kingside fianchetto, with such moves as ...g6, ...Bg7, ....d6, ...Nf6, etc. ... The lack of early central contact ... means that there is little chance of violent early contact knocking the player out of his preferred scheme. ..." - FM Steve Giddins (2003)
"... If you choose the Pirc against 1 e4, it makes sense to consider the King's Indian against 1 d4. This is more flexible and will give you additional options later. ..." - GM John Nunn (2006)
If I remember correctly, GM Seirawan suggested this sort of thing in Winning Chess Openings.
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
Also discussed in A Practical Black Repertoire with Nf6, g6, d6
https://www.newinchess.com/media/wysiwyg/product_pdf/7655.pdf
https://www.newinchess.com/media/wysiwyg/product_pdf/7632.pdf
Perhaps, it would be of interest to look at The Fianchetto Solution by Emmanuel Neiman and Samy Shoker (2016)
https://www.newinchess.com/media/wysiwyg/product_pdf/9029.pdf