For a Pump/filter, If your handy, you can use a washing machine pump, from a hoover twin tub and hook it to your own filter made from a large plastic drum with your media inside. If not so mech minded, Id suggest a largish @Eheim or fluval cannister type, which can be houses inside the lil shed thing out of rain. (be very careful with water and Electricity.
Barring that try a garden centre or the like near you, there bound to have pond pumps n filters suitable. Some of those merely circulate the water, have a fountain etc. Those could be used for circulation but wont effectivetly clean the water, thios would have to be done manually.
As I mentioned to somebody in the other pond thread, You need to take incount drainage/what kind of pond you'll use.
You will need to drain it, aleast partially from time to time for maintainence, the cement 'footage' may retain drained water, unless you manually syphon by hose or similar.
How many turtles?
Id suggest its not big enough for two adults alowwing for land area, perhaps if your getting hatchling or small turtles then you might house say 3 of them...(for a while).
Atleast half the avail space should be pond, take into account easy access to and from the water aswell, i.e ramps or better, gently sloped sides., not too rough (plastron abrasion) or too smooth (no purchase) .
2mx2m would be the smallest pond I would attempt personally, which would leave you no land room, no good really im afraid.
Maybe put a pond half the size and use the whole thing for ewd instead, replan the turtle pond.
Meanwhile you could have two or three hatchling inside instead, where you can enjoy watching them for atleast 18 months to two years in a 4 ft aquarium. by which time you can plan better and build a really optimal pond.
