Best/easiest way to prepare photos for photo book?

Displays can be much brighter than paper, so if your display brightness is set too high, you might misjudge how bright the photos are as you correct them. That will make the photos look too dark when printed.

To avoid that mistake, if you have a device for profiling your display, run it with the target brightness set to 90–120 cdm2 depending on how bright your room light is.

If you don't have a device for profiling your display, set the display to about 2/3 of full brightness.

In addition to the great points above about setting up your  the monitor, I would also add use the histogram. Our eyes very quickly become accustomed to dark or light images. The histogram shows no such apdaptivity.
Dave

Thank you, everyone.

I've decided the smartest thing is to look at each photo individually and deal with it accordingly.

You can automate process to resize images to specific dimensions and resolution. There are multiple ways of doing same thing. You can record action or to use Image Processor Pro for that task without recording action. The easiest way is to process separately horizontal and vertical images using Image processor Pro. If you want to process all images in one pass then you must record action and to deal with conditional actions.

If you need more instructions please do not hesitate to ask question.

The big question is - why do you need to change brightness and contrast? Do they print too dark? Poor black level in print?

In that case a much more efficient approach is to calibrate your monitor to actually match printed output. It's not as hard as it sounds: just make it look right. Then it is right. You can set it in the calibrator, but you can also do it in the monitor's OSD controls.

Most monitors out of the box are way too bright, and have way too high contrast range. What you want is to match monitor white to paper white. Just get a visual match. Once you have that, your prints will no longer be too dark, because you will adjust them correctly to begin with.

Similarly, almost all monitors reproduce blacks that are much deeper than you ever get on paper. This makes the print look muddy and undefined by comparison. A good calibrator lets you set the black point as well as the white point.

To answer your specific question, the way to do this is with adjustment layers, either Levels or Curves. You could also record an action to automate it.

Any one-size-fits-all method for handling 100 images of different scenes and objects implies a compromise in quality.

You will be reminded of the compromise every time you look at the album. I suggest that you correctt the photographs individually.