MN all together (regardless of the amount of MN) receive 977.4 DMD per day, right?
Yes, for all MN 977 DMD per day are allocated.
This number is divided by the number of active MNs.
The more MN the less reward for each one.
But since each MN requires 10k DMD.
It can be calculated that the total number of MNs is unlikely to get to a mark of 100, since the total number of coins in the system today is only 2.1 million Diamond.