I think it's doable, but like mentioned above, you'll need someone in a boat to watch you and to carry your gear.
If you decide to swim in Lake WA, I will swim with you as I am training in that lake as well. It's good prep, the tides just in that lake are much stronger than you would expect.
6 miles of swimming is a long way--it's about 180 pool lengths (and remember that swimming in a pool is WAY easier than open water swimming)
BTW: You can't run that far in a wetsuit, you'd have to strip it off when you are on the other side of the water and retrieve it later.