According to cephbase.org, Filosus reach a maximum size of about 15 inches overall, 7cm mantle (approx. 3.5 inches) and arm lengh of 30cm (approx 12 inches).
Yup, very day active, and more or less interactive, varying from individual to individual. My first one was accepting thawed silversides and pieces of raw shrimp from day one, as well as very curious about me as she would grab me and pull my fingers to her, and even come to me when I dangled my fingers in the water. My second one never took any dead foods, and would allow me to touch him, but wouldn't stick to me, he pretty much did his own thing. He would blow water at me anytime I was nearby, so he apparently thought of me as a nuisance. I think his eye issue might have influenced his behavior though.