Pics of the overflow, where the water drains out of the tank to the sump will be good. I know nothing about acrylic tanks so can't comment on the bowing/crazing.
There is nothing intimidating or complicated about it once you get your head around it, a picture is usually worth a thousand words so I whipped this up in MSPaint in about two minutes flat...

Hope that makes sense!
With regards to cleaning out your current filter, I would leave the biological media alone unless it is completely clogged with crap. Just rinse the mechanical stuff under the tap.
If you are having trouble with nitrates you could try Pothos plants. However, I haven't been able to find an answer on whether the roots are toxic to fish and I think there is a good chance that the uaru would nibble on them, so it could be a bit of a gamble unless you can keep them away from the uaru.

There is nothing intimidating or complicated about it once you get your head around it, a picture is usually worth a thousand words so I whipped this up in MSPaint in about two minutes flat...

Hope that makes sense!
With regards to cleaning out your current filter, I would leave the biological media alone unless it is completely clogged with crap. Just rinse the mechanical stuff under the tap.
If you are having trouble with nitrates you could try Pothos plants. However, I haven't been able to find an answer on whether the roots are toxic to fish and I think there is a good chance that the uaru would nibble on them, so it could be a bit of a gamble unless you can keep them away from the uaru.
