We install the Aquascape designs stuff.
I agree with about 95% of thier stuff, and they are probably right about the other 5% I just probably do not have enough experience.
My advice.
Buy big, 11 X 16 as an absolute minimum.
DONT FEED THE FISH... We have more problems out of ponds we install with people feeding the fish then anything else. Even after you tell them NOT to feed the fish (except for entertainment, and then sparingly.)
GOOD pumps mater.
Water makes a great level... make sure you have your level right before you put in the water or you will find your error.
Rocks are expensive. Not sure what kind of advice you are looking for particularly, but one of the things many of our "would be" customers miss, is just how much it costs to put one together properly. Do it all on paper a couple times, then add a big margin. Aquascape designs stuff is really good for this because you tend to hit all the points in planning.