Yep I went to lowes and got some sand to fix the bottom up and not use plywood. I also got some light blue foam bored for the sides...not styrafoam...I think this is a closed cell so it wont take in water. We will see how it last.
For the filter I picked up a tetra pressure filter 1500 with the 9w uv and I will run it with a mag 18 T'ed off for any excess flow. I can run 750gph through the filter outlet and the water in the pond comes in just a tad under 300gal by my measurments. I might also throw another power head in there to add some current so there will be less collecting on the bottm.
I have 2 RES now and I will probably pick up 2~4 more turtles (rio grand RES, maps, painted). I also plan to add a few koi maybe 4 ~ 6. I know the koi will be too much one day but im sure ill get a few years out of them....if the turtles dont eat them first lol. I had one of the RES with koi in another pond a year ago and he left them alone mostly....he is about 8". I wont go with baby koi so they are pretty quick. The other RES is about 2" so he has some growing to do before he catches a 6~8" koi.