I am having a noob moment.

How do i combine the following two concepts in a single command line?
#define the filename:
exiftool -p '${DateTimeOriginal}__${ShutterSpeed}s_f${Aperture}_${EXIF:ISO}_${focallength}' $1 \
| awk '{gsub(/:/,"-");gsub(/.0 mm/,"mm");gsub(/ /,"_");gsub(/\//,"-");print $0}'
#move the file to the new name
mv -n -T "$1" "{}"
....so that the result is a single filename parameter goes in, and a renamed file results.

You're having a "I'm a complete fucktard that can't use [code] tags and is still trying to do something more complex" moment.

#define the filename:
exiftool -p '${DateTimeOriginal}__${ShutterSpeed}s_f${Aperture}_${EXIF:ISO}_${focallength}' $1 \
| awk '{gsub(/:/,"-");gsub(/.0 mm/,"mm");gsub(/ /,"_");gsub(/\//,"-");print $0}'
#move the file to the new name
mv -n -T "$1" "{}"

provide sample input and output. i still use a daguerreotype and a mimeograph.