Where in the US are you?
I personally am a little dubious about the logic you're using to arrive at this configuration. Not so much because there's any giant flaw in the logic per se, it's more about the premises, which all come from a very superficial appreciation of the issues -- naturally, since you don't play accordion.
The classic French musette (and Portuguese) configuration (in my estimation anyway) is C griff CBA, but as you probably know it has a stradella bass. The stradella layout is unusual in that there's an extra bass row, and the outside row is dominant 7 but voiced so that it can serve as a diminished as well. The bass reeds may be a little heartier, too - you can really hear French and Portuguese players pounding out bass lines on these accordions, maybe just because that's how they like it, don't know. My accordion is one of these - very rare in the US - and it sure has a heavy, resonant bass.
Anyway, my take on your decision tree:
- piano or button? You'll find a lot more good piano accordions for reasonable prices, and a half hour survey of online videos should convince you that piano keyboard is no handicap for virtuosity. Sadly, to my knowledge, none come with the French style 3/3 stradella layout, all the usual 2/4. Any sensible person would go for piano. You don't have to be sensible, though, since even an accordion player is technically an artist. When my accordion fails, I reckon I will book a vacation to Europe to get another, seriously.
- C or B button? I like C and it's about as common as B. There may actually be some technical reasons why some music is easier on C or B, but don't put too much weight on these notions - it's like the button vs piano debate, but with even less to it.
- Stradella vs. free bass? Free bass is cool if you're going to play piano and organ music, and of course it's versatile, but it isn't entirely just out of inertia that so many accordions come with stradella bass. Used to chords? Do you know what "IV" chord means? Stradella is all about that, including the bass rows - the columns are III VI II V I IV and of course eminently "movable". And it has a lot to do with what makes accordions sound like they do, so if you find accordion music per se appealing, stradella bass is what you're hearing.
- Common 2/4 vs. French 3/3? Alas, unless you like the idea of a trip to Europe any time you want to look at accordions, it's probably better to stick with 2/4. It has its merits, apparently, though they are in my opinion outweighed by the obvious advantage of the extra bass row.
