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.
Stastically, that's just not true. With the two main anti-Marshall moves (8. a4 and 8. h3), White scores a good ten points better than Black at both the master and amateur levels, per the lichess database. White scores slightly better in the Italian too, but only by about half that margin.
Contrary to the perception that these Anti-Marshalls are ways of "settling," White really does still have the better chances on account of the space advantage and the active b3 bishop.
SamuelAjedrez95, lots of good points here. I'm amused, though, by a funny goof in the Jaenisch line you gave way back on p. 1 (6. Kf1?!?)
Chess is fun. My favourite opening is the ruy lopez because I win so many games with it.
Don't listen to yourself. Listen to ssctk. ssctk is telling us that we are suffering the horrible torment of Ruy Lopez theory and he is here to save us.