Well, I've got a second 370PEQ and SW-12-08 driver on the way. I don't know that I "need" a second sub, but I like the idea of symmetry, and the second H-frame is already built. . . .
Sruffle, I can answer at least one of your questions: the amp comes with around 32" of hard-wired speaker cables. I decided I wanted a bit more length, so I cut the stock wire and built a wood enclosure with two sets of binding posts (one for the driver coil and one for the servo coil). I have 4 feet of cable going between the amp and the subwoofer. Here's a photo:
In previous threads, Danny has insisted that the sub needs to be close to the amp. That's why I'm not using my one amp to power two subs. In my situation, the cable would be too long. But I don't hear any issues with my 4' cable length.