Hi
Maybe one of you knows an answere to some questions i have for some time already.

Its about playing together with other instruments/musicians.
One of the reasons why i did start again to learn playing the guitar, was that i wanted to play backgrounds for my whistling. (while i now would even say, id like to whistle something to the tunes played on my guitars)

Anyway, i know to whistle a bit, i know to play guitar a bit.
BUT What have i to know, or consider, or learn, if i want to play them both together (not at the same time ;-), one by one, record them and mix the recordings to one piece, later)

Maybe both has to be in the same, key, or pitch, or maybe better not ... surely "what sounds good, is good", but there surely are some things to consider, arent there?

What do i have to learn? Theory of harmony, composing,... i dont know.
Does one of you know?

Let me tell you 1 example
I know to play "norwegian wood" on my guitar , not just the rhythm, also the melody
and right now, i am learning to play the melody on the melodica.
But the melody of the version i play on my guitar goes "a,b,a,g,f,...'"
the melody of the version i play on my melodica goes ""b,c#,b,a,g#,..."
Do they fit together? do i have to change one?

Should i play on the guitar, instead of rhythm and melody, only the rhythm, if i want to play the melody with another instrument?
Or should i just solo with the melodica,.... i havent tryd anything nyet because i dont want to spent a lot of time going the wrong way .....
So, does one of you have experiance in playing together with other instruments?
Do You know what theory i have to learn?