For a secondary hacker, I probably wouldn't worry about the Data Processing aspect. If you only had the Cybercombat skill, you could do enough damage with just Brute Force and Data Spike, both of which use Cybercombat, Logic, and Attack.
That being said, you've got an excellent point about the Hermes Ikon (DR5) commlink; for 3000¥ you get DP5 and FW5, allowing you to use hot-sim for that +2 dice pool bonus, at the risk of physical damage, with a +4 Initiative Score advantage over the Blue Offender route. A fully specced out AR hacker may already have 4d6 initiative dice, but if not then the Hermes Ikon is a good route.
Rooks is right, too; writers have confirmed that the price of attack/sleaze dongles should be Rating2 * 3000, making a Rating 4 Attack Dongle cost 48k ¥.