I hate to sound like a crochety old man, but this sounds like a huge amount of overengineering for something that could easily be put in an ACID database to beg

I hate to sound like a crochety old man, but this sounds like a huge amount of overengineering for something that could easily be put in an ACID database to begin with. 100,000 requests/day is less than 2 a second. Most self-respecting databases would giggle at calling that a stretch. The reason I know this is that I've built and maintained systems that handled millions of ACID transactions a day. In tables with millions of rows. Uphill, both ways, in the snow. Now excuse me while I go outside and yell at clouds, because I'm surely missing something profound here.