I'm going to archive all my older tapes and disks. The tape recorder is connected to the soundcard's line-in and I use Audiograbber.

Audiograbber shows the signal level from 0 to 100% using a bar graph.

Do I get clipping if the signal goes up to 100% ?
Is it a good idea to record at a lower level (e.g. 80%) to avoid clipping and then "normalize" the wav file ?

Or if I record a disk with 95% and some Clicks exceed 100%, does that cause clipping noise in the wav or later the mp3 files ?

yes, check if the actual peakmeter values reported are correct with some other software.
no, just encode the file as it is and then use replaygain on the allready encoded file. (at least thats what i would do...)