Good you found the data 🙂
The 30,000 is my advised limit because as you’ve found sheets can get unstable when they fill up. The documented limit is 2 million cells. There are various ways to receive a notification/automation when a sheet fills up but to my knowledge they all require custom code. I’m starting some more development work in the next couple of months so this may feature.
No idea on the ods, it may be Google servers can’t cope with generating large .ods files