It's good to learn the first 4 frets, sure, but not "best". "best" is to learn the whole neck.
If I were you I'd:
Find all the notes of the key Eb in those first 4 frets, with D string fret 1 as your "base," but also: find the notes of the key Eb based around the A string, 6 th fret and see how the same key functions in a different position.
If anything, I'd suggest positions farther up, that avoid open strings, as they tend to reveal the common "movable" fingering patterns more clearly, and can be better for learning the abstract patterns of music.
(Tho personally I love using open strings...gives each key a unique feel.)