Mistakenly removed permissions
To get started, you need at least to re-install the OS. Boot into the recovery system by pressing Cmd-R on system startup and the proceed with installing the OS. This will (unless something goes very wrong) not impact your existing data

After that, you will at least have a system which boots again. What still needs to be done (and which may turn out to be a rather cumbersome process) is to fix permissions for all non-standard applications and their support/library files. Again, just reinstalling these applications might be the easiest way.