A few things -
As far as forums go, depending on what type of pond you want, for a koi pond with mostly mechanical filtration, have a look at
www.koiphen.com
For a garden pond (mostly wetland filter type plant filtration), have a look at
www.gardenpondforum.com
6 feet deep seems overkill for your climate. It can be difficult to provide good circulation at that depth, servicing a pond that deep requires draining the pond somewhat, and that deep of a pond will add to liner costs. (I'm assuming you're thinking of a liner pond, not a concrete one)
45 mil EDPM liner plus underlay will probably run about $1/sq. ft.
Laguna pumps are a great choice for a submersible. They are energy efficient.
If you decide to use an external pump, they are easier to service, but can get expensive depending on your setup.
A lot depends on what you want for a pond.