A couple thoughts, my boat is a Tolman and not as big as a great Alaskan. My deck will be non self bailing so the bilge pump will have to deal with spray, rain water, and fish guts in addition to unplanned water. Some of this might not be as important if you have a self bailing deck and don't plan on your bilge pump running often
-I'm going to have a discharge on each side with the idea of the boat listing to 1 side the other side might be able to work, probably a false sense of security and you are all ready screwed if you get to that point. Hoses for each pump will be long enough to reach either side
-I want both pumps on float switches, with a non self bailing deck and southeast Alaska rain the primary will cycle every once in a while in the rain and there would be a lot of water in the bilge before you noticed it was time to cycle the pump unless you are checking every 15 minutes.
-I'm using a Johnson 1000GPH with the replaceable gut pack as my lower primary pump with their float switch. Thanks a hack mechanic on my current boat I have a spare gut pack and float switch. The gut pack is easy to change/ clean. My spare gut pack has ring terminals on it to make it easy to swap in an emergency. A complete 1000 w/ float switch is $76 and I'd consider it a throw away item possibly replaced yearly. These pumps are 3/4" output and my secondary pump will be a bigger pump with a 1 1/8" hose. Rule makes an adapter so the smaller pump can use the bigger hose.
-My current bilge pump has a float switch and a manual over ride switch with a light on it, when the pump is running off the float switch the light still lights up so I know the bilge pump is running. Usually it cycles for maybe 30 seconds. If I notice it on for longer it's time to investigate.
-I've thought about wiring the secondary pump to an alarm possibly with an alarm bypass switch to get my attention
-Ultra Safety makes really nice bilge pump float switches though they aren't cheap
-Both bilge pumps will be wired to the float switch pre battery disconnect to the house battery. Blue sea makes a nice ignition protected stud mount fuse block that bolts right to the battery. I'd like to still have the motor battery charged if a bilge pump gets stuck on so I can still start the motor.