The answer is: A lot!
There are no hard limitations, except 2 Billion distinct values in each field.
The "soft" limitation is that the QIX engine needs to be able to load all data into physical RAM, which means that if you can equip your box with a large amount of RAM, you can load hundreds of millions of records.
But - 50gb of text files every day sounds to me as if you soon will reach a limit. So, you should consider ways to partition your data or pre-aggregate it. One app per week/month? An overview app? etc.