I would add one thing to the answer above which is well presented and quite comprehensive.
With regard to transmission mode, The UE is given the transmission mode in the dedicated portion of the RRC_Connection_Setup message.
So the way you should think about it is: You can certainly determine the number of antennas from the CRC on the MIB, and if the eNB has more than 1 it is required to use transmit diversity for broadcast, PDCCH, and SIB messaging.
You'll be instructed what to use based on the DCI and your assigned transmission mode. This does not need to be blindly determined.
It's a small nuance.