Looking good Dan. I like a koi pond with plants!
As to the filter, forget the foam! You'll be cleaning it so often you'll be swearing and cursing every week. Go for a static K1 filter in a water barrel. It will still need regular cleaning but that involves turning an air pump on and then pulling a valve!
What you need to do is have a pipe going into the filter from the pump (I'm assuming your pump is a solids-handling one?).
Then your return from the filter needs to be a 4" pipe up near the top of the filter with slots or 8mm holes drilled in it to allow the water through. This pipe goes through the wall of the filter and returns the water to the pond or next chamber of the filter.
You then fit a 1.5" fitting right at the bottom of the barrel with a slide or ball valve on it that will be your waste valve. (This is best attached to a long piece of pipe with holes in to water the garden - it's great fertiliser.) You need a short section of drilled or slotted 1.5" pipe to stop the K1 escaping onto your garden!
The last thing to do is fit the pipe that will deliver the air for cleaning. The best thing to use is Speedfit plumbing pipe with 2mm holes drilled in it. About 10 holes should do in a ring about half the diameter of the barrel's base. You can then get a cheap diaphragm air pump off Ebay and this should come with a rubber fitting that will go straight onto the Speedfit pipe.
Finally add about 50l of K1 (again available cheapest off Ebay when I last bought some).
All you do to clean this filter is this;
Turn off the pump (make sure the pump isn't set up to drain all the water out when you do this! - drill an anti-syphon hole where it comes above the water line).
Allow the water to run out of the filter for a minute or two.
Turn the air on.
Allow the K1 to boil and spin around cleaning the K1 for about 5-10 minutes.
Pull the drain valve to send the dirty water to waste.
Turn the pump on to re-fill the filter and repeat the clean with the air pump.
Drain again.
Turn off the air and turn the pump back on to start filtering again.
I know all that seems a bit complicated but it really isn't. There are some pictures of the same kind of thing on this page here that might help you get the idea,
http://www.happykoi.co.za/filters/duo_filter_systems.htm.
Also don't raise the pump off the floor of the pond. You want all that detritus out of the pond, not sitting on the bottom going anaerobic and festering and raising the levels of Aeromonas and other nasty bacteria.