Your pond is looking good!
That pump should work great, it is a nice size for what you want.
If you want to go with a filter, this is one of the best DIY filters out there http://www.koiphen.com/forums/showth...t=s%2Fg+filter
, and this forum has info on everything. In the spring there are a lot of growers that have pond plants very cheap!
One of the best filter plants for a pond is water hyacinth, they do best if you put them on a gravel or dirt substrate.
I would go with goldfish and not koi, they will eat or kill every plant you have sooner or later.
One thing you need to make sure you do is make the liner edge well above the rain water runoff line, I made this mistake and had to redo it!
Building a pond is a lot of fun!
Here is a pic of my water hyacinth I started with five and in two months this is what I got.
They have a wonderful bloom to!