Cheers, it’s my pleasure to assist where I’m able.
Most modern tsugaru bachi are in the 14~18cm spectrum, usually sporting a bevel where the handle transitions into the blade. Min’yo bachi tend towards 20cm and generally lack the pronounced slope into the blade. When made, they will usually be wider than a tsugaru or nagauta, but not so wide as a jiuta.
A sampling of various genres, from the shinnai/kouta kobachi to the gidayu mammoth
Various classical bachi demonstrating the profile of nagauta vs jiuta vs gidayu
For repair ideas, you might look at the Building/Repair sub-forum. While I’m familiar with the instrument itself and a good bit of its background, I’m no luthier.
At 21.5 x 20 (approximate), it’s at least go-bu-dai (the standard dimension for tsugaru).
Here is a link to body dimensions, converted into metric if you wish to more precisely class it.
You can also find some excellent resources for learning (in Japanese) by looking on youtube. One flat positive of the pandemic was a virtual explosion of professional players embracing the platform for performance and teaching.