Math seems right but honestly, I don't bother making small amounts. I do 10L mix at a time, kept in 5gal Doran tanks with floating lids. I spray some developer preservative in the dev container at end of each session. I dont use the blix additive. I keep the 2L tanks solutions in soda bottles between sessions. 6 weeks is nonsense, I have used it for up to a year as stored above and it is fine. The stuff is cheap enough that even if it didn't store well I would still do that.

For color heads consider the beseler minolta 45a. It is a great head, additive color with a fantastic analyzer built in. Usually in the 100-200 dollar range on ebay. I have 6 of them (5 spares), bought mostly as insurance and it is cheaper to get the flashtubes that way and have spares to boot.