Put on a life jacket, pour a rocks glass 1/2 full of Dimple Pinch... neat, sit on the edge of the pond wall with your feet dangling in the water, and sip the scotch slowly...
Much more pleasant than Lithium
Point being, give yourself the chance to enjoy them a bit more, and stress out a bit less. A little personal "down time" with your wet pets will help to clear your mind of all the stress and self imposed pressure and help you make good choices for your pond.
Running too far ahead of yourself can be just as frustrating as letting things get out of hand, and it sounds like you've been sprinting. Koi are a lot more like a marathon than a series of 100 yard dashes, so you need to pace yourself. Your TT ideas both sound fine, so I doubt there is a bad choice to be made there. Build one, let it run a while, and then see if you really need a protein fractionator.