romanr,acquiring that 2000 GPH pump sounds like a good plan, especially since it is on sale!
Though I can't tell you if it is a reliable pump or not as I have not come across that brand name?

Laguna pond pumps, Pondmaster pond pumps and Little Giant pond pumps, are reliable pumps and you may find them on sale at this time of year. Do a search and it maybe worthwhile to you.

The "rule of thumb" commonly advised, is to turn your pond water over once to twice per hour, so you will be well within those specs with a 2000 GPH pump, even with your piping lengths there will not be a great loss in the flow rate.

The bonus about having a greater output from the pump than you really need, is that you have the volume already there, should you need it in the future.
Once you get the pond bug, you will probably want to go bigger and better, like a great number of us did.

You can install a ball valve on the output side of the pump (never on the input side!) to control the flow to what you want, it will not harm the pump in anyway.
Good luck with the project,
"Horton"

I read a few reviews with the link you provided. Sounded like most people had problems with the pump. Also wonder how much electricity it uses. I would look at some of the brands Horton suggested. DC

It looks like it may be a brand made for Lowes. Not sure though. It also appears to be an energy hog, at 1/4 hp! I have an external pump that is 1/16 hp that pumps 3600 gph. So I really don't think you are moving much water for the amount of electricity it uses. I have had great sucess with Pondmaster pumps (several of mine have been running 24/7 for over 10 years now).

From the recommended brands Laguna has the most user-friendly site but after reading product characteristics I got a bit puzzled. Need your help. To remind you: the pond is about 500Gal and the waterfall starts at 8' high and 15' long.

1. Pump. My understanding is that I need the 1500Gph pump as the next lower volume pump is only 900Gph and probably not powerful enough for pond height and length.

2. Filter. PowerFalls Filter Spillway matches my desired width although I didn't find data about its throughput.

3. UV Sterilizer. a) do I need it? b) there are few models but all with 500Gph. Since I'm planning for twice as much what do I do?

Thanks in advance!

Here is a link that might be useful: Laguna site

Horton has given you good advice. Even though your pond is 500 gals. with water turnover twice per hour is a 1000 gph pump. The challenge is you are pumping up 8 ft which is head and your pipe length is 15'. Anything I've read is allow 100 gals per inch of waterfall width which you didn't mention. What you do need is a pump that is capable of pumping 1000 gph at 8ft up. The size of your pipe also comes into play as there is more friction loss on smaller pipe diameter. There is also friction loss with fittings--90's etc. Sounds like you are looking at a submersible pump. I started with those but didn't like having to drag them out of the pond to clean also by the time the water went through the 1 1/2" pipe to my waterfall which is only 4' high and pipe run 15' the flow was only 700 gph on the waterfall-that was from a 1950gph Little Giant pump that used 330watts. So you need to look at friction loss/head charts for whatever pump you are buying.