What are you thoughts regarding these upgrades to the electrical system?
In my 850, the current wire from the alternator runs below the intake and does make sense to add
another cable when I need to remove the intake for the PCV system.
It makes no sense to do it just because someone coined it "the big 3".
You need to analyze which circuits are drawing more power, how much additional loss that is, and whether that is acceptable.
A simple multimeter measurement of voltage at both ends of any connection can tell you how much loss it has and whether it needs improved, but keep in mind the needed improvement might just be cleaning off terminals, or new ones if the wire to terminal connection has oxidation or corrosion, not always redoing the whole wire run, except of course you almost always want a new lower gauge run back to a sub amp.
As far as the alternator wire, it should come from the factory sufficient to handle the full alternator current. If you upgraded the alternator, then upgrade the wire proportionally. Any wire, you can take the gauge and length and calculate the voltage drop or just consult a chart, keeping in mind that if it is a chart for copper wire and you buy that cheap copper plated aluminum junk, it won't be capable of as much current.
does make sense to add another cable when I need to remove the intake for the PCV system.
We'd have to see pics to know for sure, but odds are that it's not a big deal to just disconnect the alternator wire once in a blue moon when your intake needs taken off, should easily be less work to spend a minute doing that a few times rather than making a custom cable for it.