Excellent stuff, that what I was thinking for my tank, either 2 filters like Fluval 305/6 or 1 large filter like Tetra Tec Ex 1200 or something like that.
2 externals makes sense though, if one fails or has a problem you at least have a filter going that would just about cope for a little while.
Also you can alternate maintenance clean each filters in turns so the effect is beneficial.
Rock formation simply done by forming them in a pattern you liked and then silliconing them into place. I do like that!
Very well done on a pretty decent set up.
Keep up the good work and post pics when the water has completely cleared. Bet it will look good.