Quite a few questions raised... I'll try and answer most here.
- The acceptance is usually by email in a standard format, along with terms of how long you have to accept etc.
- Yes, it's about 10d that you get. I think there is an amount of flex when this competes with Stanford, but that's usually working the other way around.. i.e. people admitted to Stanford who are trying to delay decisions till they hear from MIT. The payment to confirm your place is 10k usd, and they usually put in a specific date for that.
- I'm not 100% sure of the number admitted so far, but I'd say it's easily about 60+.
- Fyi, a lot of people seem to have applied at both MIT & Stanford, and both schools 'lose' candidates either way, depending on various factors...
Hope that helps... good luck!