Thanks for your interest in Cursor business - to answer your questions:
You can invite as many accounts as you want to your team, with no upper limit. Each user you invite is charged at $40/month.
Each user gets 500 fast requests by default. You can increase this by batches of 500, for a further $40/user/month (e.g. 1000 requests for 10 users would be $800/month)
If you keep Claude 3.5 Sonnet selected once you use your fast request, your following prompts will still be answered by Claude using the slow requests.
If you swap to a smaller model, like 4o-mini, your queries will still be as fast as always!