There are some Harmony remote users around here who can offer a better comparison than I between the 720 and the 890 - I'm not even sure what the 720 might be lacking aside from RF in comparison to the 890 (it's no longer listed on Logitech's site). If your equipment is concealed, the RF could certainly come in handy, but you'll need IR emitters to deliver those signals to the equipment (the 890 does appear to include the RF receiver that has a half-dozen or so IR outputs).

If the cables are directional (the arrow indicates at which end the shield is grounded, typically), the arrow should point in the direction of the signal path. For a connection between amp and 990, that direction is from the 990 to the amp and the arrows should point toward the amp.

If you are talking about having pictures appear in the body of an e-mail instead of simply as attachments, you'll need to have the e-mail formatted as HTML or rich text rather than plain text (I prefer plain text myself, but some of that may be a vestigial tendency from the days of using pine to check e-mail on the university server).