I am NOT claiming credit for this, someone else showed me one first!
32 water mills, 1 retriever, 1 deployer, 1 filter, 1 thermopile, 1 bucket lava, about 10 water and around 36 buckets (forgot to count)
With a 1s tick rate it averages about 36EU/t, peaking at 64EU/t if allowed to idle.
With a 0.5s tick rate it looks to give 64EU/t.
The thermopile appears to have no difficulty powering 1 retriever, though it takes an AGE to charge before it will start.
PS yes the water source isn't quite infinite and it dried up when the chunk reloaded-modified. Also it might run better with a sequencer, It can logjam if there are enough empty buckets in circulation.
It might help to put a restriction pipe after the retriever, as if a full bucket backstuffs it can sometimes stuff the retriever, making it unable to remove empty ones and causing a jam, instead of stuffing the filter.
Safest solution is to put one bucket in each mill before switching it on.