As soon as I have a few Kekimurus I can't keep up with cake production and eggs are the bottleneck. Everything else I could scale up quite a bit. I tried to add more chickens but the server-process really didn't like that and couldn't keep up anymore at all.

I know this is different than cows giving milk, since you can milk them as fast as you want and chickens only lay eggs every once in a while, but on the other hand, if this game wasn't programmed in Java, I could just add a bunch more chickens. So that isn't an intended limit.
I'd really like to make the Kekimurus work, since it's something fun and different compared to the usual fuels that generators use, but at the moment it seems that my best bet for mana production is actually to dump the tons of coal, my ender quarry gives me, onto a bunch of Endoflames.