For the Ruy you need
something for the Marshall
to learn to play the Open
to learn to play the Berlin endgame
to have something for each of Chingorin, Zaitsev, Breyer
To have something for sidelines ( cozio, Schliemann etc etc ).
That's a lot more compared to the Italian. I'd say start with the Italian, which is simpler, and then later migrate to the Ruy ( e.g. you can start playing a Ruy here and there when you know what your opponent plays and have already prepared for it ).
This is a matter of precise knowledge vs intuition. The way you talk about learning openings is that you have to learn exact memorised lines to be able to play an opening. This is a substitute for simply playing well and understanding the opening.
There's no need to complicate it.
In regards to all the variations you mentioned, this can be learned in under an hour: You don't even have to learn the Marshall Attack or the Berlin as you can play anti marshall and anti-Berlin lines.
I arranged this in a under a minute.
For some of these you do need memorised lines, eg the Marshall.
It's possible to play an anti Marshall, it's also possible to play an Italian, neither promises an advantage and both are good openings.
Preparing for the Marshall in under an hour is a false assumption. One can probably watch a couple of YouTube videos in that timeframe but that's different to preparing for it.
For the Ruy you need
something for the Marshall
to learn to play the Open
to learn to play the Berlin endgame
to have something for each of Chingorin, Zaitsev, Breyer
To have something for sidelines ( cozio, Schliemann etc etc ).
That's a lot more compared to the Italian. I'd say start with the Italian, which is simpler, and then later migrate to the Ruy ( e.g. you can start playing a Ruy here and there when you know what your opponent plays and have already prepared for it ).
This isn't entirely true. White can also just learn the d3 Ruy Lopezzes instead of unique setups against every different Black plan.
4. d3 avoids the Berlin endgame and is a decent setup against the Schliemann.
The Anderssen (5. d3) avoids the Open Morphy, and the Duras is a unique plan in case Black doesn't immediately play b5, and if Black does play 5... b5, then this transposes to the Martinez (6. d3), which will usually transpose either to an Arkhangelsk or a Closed Morphy. The omission of an early c3 allows White to play an early a4 or to play h3 before h3 and limit Black's counterplay, while coming at the small cost of losing a tempo if White decides to play the d4 push later in the position.
It's possible to play the d3 Ruy to avoid the nature of some of these lines, it's also possible to play the d3 Italian, they're both quality and with a similar goal, first play d3, and then later play c2-c3 and d3-d4.