Not knowing your background with these instruments, let me offer the following:
These guys are using 1 row and 3 row accordions commonly.
There are two keys that are very popular for the 3 rows. The 3-row players
would need to chime in here to tell you more. (I would think you'd want a
3-row who's first row is in "F" to match BooZoo's rendition of "Paper in my Shoe")
For single row, the most popular key is "C".
But, you generally want to play in second position if you want to play
any blue notes. Playing second position on a "C" accordion give you the key
of "G" with a flatted seventh "blues note".
For example, the BooZoo clip that you had posted is obviously being played
on a 3 row.
You could play this facsimile of this song on a 1-row. If you wanted to match his
key, I'd suggest an "F" box single row accordion and play in second position which
is "C".
YOU COULD also play this on a "C" accordion, first position, but I personally
wouldn't do that because it's "unnatural" in terms of the difficult fingering
that it would require.
Point being .. there is a bit of music theory going on here and you are correct..
you do not want to purchase the "wrong" key for what you're playing :)
Also, from my experience, I don't think I've ever met a Cajun Player who uses
sheet music. It's all done by ear, so you're on the right track with that idea.
Tom, he said he can't read it or write it. It's not his idea. And sheet music can be a very useful tool for some musicians. Whatever works has to be a good thang. Right?
Well I went & read up on how to read & write music & I remembered studying all that stuff years ago. It still doesn't help me to know what cajun accordion is being played in any given song however.
I had thought about getting a 3 row accordion but they generally do sound a bit muffled compared to the cajun accordion. If I do get one I'll take the cover plate off the treble valves so that the sound is much clearer. It's like my piano. Normally it just sounds like a piano but when I take all the panels off so the cast iron harp is exposed then the sound is ten times clearer with more overtones.