> -1- how can I restrict the access 
> of a certain user such that he can only see certain logbooks. 

This can be achieved with the "Login user = ..." option.

> But also not showing the other logbooks on the selection page.

You could try to use "top groups". This gives you "separate" groups of logbooks, so you could make a public tree
seen by everybody and private trees only seen by a few people. Please read the documentation for details.

> -2- How can I have a login page instead of the logbook selection page.
> When I insert the password statement the config, I get a blank page.

You get a login page instead of the selection page if the "Password file = " statement is in the [global] section
and "Protect selection page = 1". You might have to delete all cookies in your browser if you move the password
file statement between the [global] and the logbook sections, because otherwise the old cookies might prevent you
from logging out.