You asked about reuse, etc.:
Ilford states you can reuse a litre of stock Microphen for ten rolls adding 10% development time for every next roll. Many photographers find that too much (high contrast) after a few rolls, so some users prefer 5%, and some others establish their own systems. There are formulas for replenishment too. I tried both -reuse and replenishment- and I didn't enjoy them, and I saw no real visual benefits. I like discarding what I use, even stock after the unusual push to 3200.
My personal use of Microphen some years ago, and my reasons for liking it, are different. I do three things with Microphen: I use it to get sharp present grain from Tri-X, so I push it to 1000 at 1+2. I use it a second way, though, for a different reason with TMY at 1000 too, also 1+2: grain is then much smaller than with Tri-X, and this is my most common use, for mixed scenes, so I use Microphen's speed and contrast control, to be able to get sunny scenes too, in the same roll, with decent shadows, because 1000 with Microphen is not a strong push, and TMY's film design is, for this, more appropriate than Tri-X, which at 1000 is better for overcast, but inferior for portraiture. The third thing I do is enhancing grain seriously for certain scenes without skin, with sodium carbonate added for higher temperature development, and it works with many films.
Don't worry if you don't use your Microphen for the zoo project: you'll find several different uses for it in the future.