winter planning for spring

Hi,
I put in my pond this past spring and now I need to make all that
changes I wanted to make this summer and ran out of time
1st thing is, because of budget, I had to go with a cheap home depot
special sump pump for the pond. I would like to upgrade. I think I
would prefer an external pump and I have heard great things about
sequence pumps. Pond is 3 1/2 feet at its deepest. about 1200 gallons I
estimate. What would be a good pump? What is the best way to plumb it,
that is where do I run the intake to etc. Berfore I just had the sump
sitting on the bottom of the oposite side of the pond from the
"waterfall"

2nd thing is the "waterfall" is not a waterfall at all but just the
water flowing out of the filter into the pond. I will be building a
skippy fiter and want it to run into a waterfall. Heres what I begining
of last spring.

http://miltonsoffice.com/pond.jpg
based on my best guess its about 1200 gallons
Any suggestions?