Just in case you missed it, from The Things Network 2016 Update, emphasis mine:
Fair Access Policy: Practice
- Golden rule: 30 seconds air-time per device per day
- For 10 bytes of payload, this translates in (approx.):
- 20 messages per day at SF12
- 500 messages per day at SF7
- more for SF7BW250 and FSK (local-area)
- If your application requires more bandwidth, think of another solution
- This allows for >1000 nodes per gateway
- Downlink bandwidth is even more restricted
- you can’t send all messages as ‘confirmed uplink’
I don't know what the actual limit might be.