Yes, all diatonics are layed out the same way, relative to the key. This is especially true of the central octave (holes 4-7). Some experiment with different notes on the lower, incomplete octave (holes 2 and 3).
The easiest thing for a beginner is to get a C harmonica, and seek out tunes in the key of C (or A minor). There's lots of those.
In addition there are lots of songs written in harmonica tabs - replacing the notes with hole numbers (usually negative number for sucking). These are easy for the beginner to use, and they avoid most copyright issues.
The toughest thing for a beginner is producing single notes, as opposed to the 3/4 notes of a chord. By the time you master that you should be comfortable with both tabs and the C scale.
At some point you'll want to play tunes in another key, such as the easy ones F and G. The main value to getting a harmonica in a different key is that you can then play with others. But for your own practice, transposing will work just as well. You might start doing this on paper, converting, for example, the notes to tabs.
Most computer programs that handle scores will do the transposing as well. I'm most familiar with
do-re-mi notation is used in two ways,
movable. In some languages, like Spanish, it is an absolute pitch, where
do is our
C. But in English it is often used in a relative sense -
do is the major key root. A diatonic harmonica, in any key, can be played in that movable sense.
With a tuner app set to solfege, the notes on my C diatonic are:
1 2 2 4 5 6 7 8 9 10
blow: do mi sol do mi sol do mi sol do
draw; re sol si re fa la si re fa la
But viewed as moveable solfege, all other keyed diatonics have the same (relative) notes.
In tabs the middle octave, regardless of key, is
4 -4 5 -5 6 -6 -7 7
la are missing in the lower octave, but can be played (in theory) as bends.
si is missing from the upper octave.
A chromatic has (typically) 3 octaves, each layed out like the middle one. Pushing in the slide raises each note semitone. It can handle all keys in those octaves with about the same ease as keyboard.