You have a similar use case to myself. I've tried replenishment - which is possible and some people claim good results using - but I think it requires more and more regular processing to be viable. Replenishing the fixer and the developer, and only using the working solutions every other month, resulted in very inconsistent processing output. Wonky colors, streaks, etc. I find I get much much better results if I mix fresh developer and fixer for every batch I run. Bleach I have been replenishing.
Regarding capacity, I am noticing that after about 4 rolls through 1L of dev working solution, stuff starts going out of spec again. Going forward, I am going to limit myself to 5-6 rolls per 1L developer.
Shelf life of the developer replenisher (which is what you mix up to be 5L worth of stuff) is quite impressive. I've kept mine in a wine bag for at least 8 months and it seems to be fine.
Take this with a grain of salt as I am still quite inexperienced with all this.