Hi there. I can’t answer your craft questions, but I am one of the resident “spent too much time researching” nerds floating around. Sooo!
Let’s talk shamisen subtype.
Hosozao, chuuzao, and futozao are broad classifications of neck width. This, along with body size, are the primary indicators of shamisen type.
However, the type of your shamisen isn’t really a limit on the kinds of music you can play, merely on what the expected sound might be.
A quick note on neck size: shamisen necks often, but do not always, taper as one approaches the tenjin/peg box. A shamisen that clocks in at a miniscule 2.3 cm near position 1, might be 2.5 at position 18.
Hosozao are thin necked instruments that range from 2.3 - 2.5 cm wide. They are most commonly found with nagauta sized bodies, but occasionally have go-rin-dai bodies.
Chuuzao are middling thick necked instruments. The usual range is 2.5 - 2.8 cm.These instruments usually have go-rin-dai bodies to ni-bu-dai bodies. A subtype of chuuzao is the tanzao. It is 5 to 10 cm shorter than a regular neck, but otherwise the same. Tanzao are generally found with go-rin-dai bodies and are used in min’yo with particularly high tunings.
Futozao are the thick-necked variant. They range from 2.8-3.5 cm wide. Futozao instruments generally have san-bu-shi-rin-dai or larger bodies.
Note that 2.8 appears in both chuu and futo classifications. In addition to the aforementioned tapering, futozao shamisen have tended to become wider over time, but older examples will tend to be more narrow.
As stated, the relationship between the neck and body will tend to indicate and instrument’s “preferred” genre. The smallest standard body is termed “nagauta” and the largest standard is go-bu-dai. Body nomenclature is based on the size difference relative to nagauta. For example, a go-rin-dai shamisen body is 5 (go) rin larger than a nagauta body.
To convert that to cm difference, you’ll need to look up the traditional Japanese measuring system of sun - bu - rin. It’s delightfully annoying!
Please note that larger sizes do exist (roku-bu-dai and so on), but they are relatively uncommon.
As a quick reference: nagauta is most commonly used in nagauta, go-rin-dai are used in kouta and min’yo, ichi-bu-go-rin-dai and ni-bu-dai are used in jiuta, and san-bu-shi-rin-dai or larger are used in tsugaru.
The other eight or nine genres (shinnai, gidayu, and the like)their various substyles (fujimoto, Sato, Chikuzan), and regional identies (Akitajamisen, Kyojamisen) all have their own specifics and preferences, but that’s beyond the scope of this post.