i think each pump should have its own outlet.
if one pump dies water will just recirculate in the bilge.
Yes, you want to run two seperate lines.
I had a barmount switch for a while, then it went bad. I will probably pick up one of those rotary switches tho. Right now I have a male/female plug right by the batt that I hook up before heading out.
The Wallywold pump has a base piece that you can glue down and then snap the pump on that. The 3m stuff is not necessary, any epoxy should work. I would also get a piece of 80 grit sandpaper and rough up where the base will be glued down. Actually I would sand the bottom of the bracket as well.
I have run both Rule and Attwood pumps. I have found that if you leave the Rule pumps running constant, they burn up. Attwood also has a 3 year warranty!