All good stuff though Photoshop is one of the few programs that can accept
16bit (48-bit for RGB) With my Canon film scanner, for example, you don't
get that option at all in the Canon software. And of course there are only
basic things you can do in PS while in 48-bit mode.
In general with image editing software I would recommend a user do a direct
gray scale scan and compare it with the conversion of a colour scan in the
image editor. I recall some early Microtek scanning software offered to do
a gray scale scan using only the "G". Some image editing magazines, such as
Design Graphics, have had some good articles on getting the best gray scale
conversion from colour.
I wouldn't personally use the brightness control since the levels command
in PS is far superior.
I haven't done any work with JPEG2000 but apparently it also offers a
non-lossy option. I have been told that theoretically there is a non-lossy
option in JPEG but that no commercial software includes the option. Whether
non-lossy level JPEG2000 is much better than LZW remains to be seen. Adobe
actually offer JPEG compression within TIF but that is non-standard.