There is probably a comprehensive article somewhere, but the answer is sort of this.
The maximum size of any table is 500 MB. if you have an existing table now and check its size in Settings, then App Management, then Application Statistics, you can do the math to see how many more records it will hold. ie if you are at 10%, then you can hold 10x more records.
But performance is another issue. If you have a table with few relationships and few summary fields, you might get up to 1 million records, well 500,000 for sure. But a complex app with lots of fields and relationships may start to suffer performance issues at 30,000 to 50,000 records.
It's a bit hard to predict. QuickBase currently does really well with tables of tens of thousands of records, but will not usually perform when you get up to 1 million records. There is no particular limit on the number of tables.
