mit innigster Empfindung is a term employed by Beethoven on a number of the later sonatas. "with innermost feeling" is a slightly more accurate translation I think.
a lot of german words are built from smaller words. zurueck means back, and halten means hold or stop, therefore zurueckhaltend means holding back, or restrained.
etwas translates literally as "somewhat" but the connotation is "quite," ie not as much as "very," but certainly more than "a bit."
been a while since I've spoken any german, I'm a bit rusty!