jbe, in response to your questions:

Depending on the amp draw, 8GA or 10GA may not be enough. To give you an example: a popular Spal dual fan combo is P/N 30102052 and consists of dual 11 inch, 5 bladed paddle fans. At 0.6 inch pressure drop (basically the resistance through a thin radiator), they draw around 33A. Thicker radiator cores will draw more amps, so keep that in mind. On top of that the 33A draw is especially bad at idle when the alternator isn't spinning that fast. I don't know what all of your electrical loads are, but I ran 6GA cable from the alternator through a 150A fuse to the positive lug on the starter relay (which is connected to the battery).

Your idea about having one fan running all the time isn't bad, and only controlling the second fan with a temperature driven relay will definitely help lessen the "shock" of 2 fans kicking on simultaneously. I use the Dakota Digital controller that you mentioned to perform in a similar way. I set the one fan to come on at a low temperature and keep it running basically all of the time. The second fan just kicks in when the first fan doesn't cool enough (usually when idling).

I ended up with the Derale 16833 shrouded fan kit because it fits a 26 inch wide core pretty well. Beware, the fan cfm specs that Derale give are overblown! They claim 3750 cfm, but there's no way that's possible. I contacted the fan manufacturer about the fan specs and each fan is only capable of 1346 MAX cfm. So according to my math, that's around 2700 cfm total. Gee, that seems a bit less than 3750 cfm ...

I tried various mechanical fans. Different diameters, number of blades and blade pitches and none of them cooled my engine well at idle. The best combo was the 18 inch, 7 bladed Mopar fan with the thermal fan clutch. Even that fan wasn't enough to keep the temperature from creeping up at idle. There's nothing worse than watching the temperature gauge slowly creep up while you're sitting in at a stop light.

Hope this helps