I have not owned a hydro syatem yet, so don't spend any money or time based on anything I say, but I very much desire a hydro-site for my retirement, so I am following your posts closely for my "hydro file".
Whether you are making a PMA from scratch or adapting a PMM, once you apply a load to your Banki, it may slow down a bit, which throws off your voltage generated calculations. Then you would have to use a smaller load (smaller gen?) or a wider wheel to add torque. Of course, only if you had enough flow to work on the extra width of the blades.
If I understand correctly, low battery charging can be as high as 10% over pack voltage, so for a 24V pack you are aiming for about 28 volts? Apply "some" small friction load to the output shaft, and then measure RPM's, then you can find or make a PMA to make 28 volts at that RPM.
A large water wheel has a rim speed of about 80% of the water flow speed, but if your Banki has the flow choked down to create a "jet" effect (like a Pelton?) I couldn't guess how it would effect RPM's, or even RPM's under load.
If your gen is too small, you are missing out on Watts that are just flowing through you fingers, but too big and it will bog down the water turbine and drop RPM's and voltage output. The turbine should use 80% of your water flow, and the gen should be sized as big as possible, but not so big as to bog down and slow the turbine.
The wonderful thing about hydro is that once you get it dialled in, the output can be fairly steady 24 hours/day. You can even increase or divert flow to affect RPM's/Volts, such as an equalizing charge or lowering input amps as you near a full battery.
Don't be concerned about using wood. You may end up making several changes to the diameter and width before you are satisfied. If it works well, you can make a better non-wood final version before the first freeze. The wood parts can be a pattern for you.
If this works out well, you might size one Banki for minimum annual flows. Then you might have a second or third one to take advantage of the heavy spring flows with snow-melt and rain.
Best of luck!