Key signatures, transposing, staffs - insights

[romagister]

After looking for sheet music for "Hijo de la Luna" and seeing this very nicely harmonized one:
https://www.scribd.com/doc/8511963/HIJO-DE-LA-LUNA
I tried to play it as is, in the 4# key of E Major (really, C# minor) - and no way my fingers can superpose the white-black-white jumps in real time... however, just trying revealed some insights and a workaround:

- Each 2# in the key are equivalent to 1 tone shift (= 2 fifths - 1 octave)
- So, a true "transposing by eye" to the no-accidental A Major is easily done by just reading 2 steps below (which doesn't reverse the line/space coding - that would throw me off worse). Which is nice because:
- There is already a 2 step coding difference between the normal bass and treble clef !! (e.g. C5 is 3rd space on treble staff but C3 is 2rd space on bass staff). So, just read the C# minor original bass clef using the treble clef decoding, and it's in A minor ready for play as it is !
e.g. see a C (# implied) on 2rd space, which would be an A in the treble clef.
- Finally I understand the beauty of the "moving all #/b near clef" to let in the score only the #/b which are really "accidental", not in the key. Transposing back would have been a PAIN if having the part-of-scale #/b scribbled in (as I have to resort to play an awkward key as-is).

For 4b (Ab Major or F minor) it works the other way around "read treble clef using bass clef decoding".

So, I got yet another shortcut/workaround to avoid the main problem... just trying to play in any key. Do you think 'normal' piano players (higher-lever amateurs, not pros) just solve it by bashing with massive hard work only ?

The 2# (D Major) as in Pachelbel's Canon original still remains a problem for me. I read many easier variants in C so know well the chords, changes, arpeggios, variations on theme etc. but, say, the white/black shifts in 3rd sequences still overload finger control.
D Major would be closer to learn the classic way, by practicing up to internalizing the 1# scale, G Major (F#) then modifying the 2nd #, C#.
And the shortcut by 'transposing by eye to C' works less well for me because 1 tone would reverse the line/space coding.

brrr... I've found another, even nicer "Hijo" but with 3b (C minor)! and no shortcut seems to work...
https://www.scribd.com/doc/6132468/Mecano-Hijo-de-La-Luna

any other such feasible stories of 'ways and means'... ?