I’m pretty sure Firebase doesn’t have any significant limitations. You’re talking about storing 1,000 rows of data. That’s a small amount of data for any database to hold.
It can be a little hard to find updated info about using Firebase with Thunkable. It’s pretty straightforward in the sense that, for example, if you want to save “hello” at /Users/userId/abcde then you would set cloud variable “Users/userId/abcde” to “hello”.
You can see a very simple use of this here: Cloud variable not storing in firebase - #6 by tatiang