Know that, I do not
It will be very difficult to predict the actual people using steemit because a lot of people have different steeming routine. Some people may steem today and not steem the next day and vice versa. Though this can be guessed be taking the average of the people that actually post in a given week.
It's difficult to know. A lot of people have multiple accounts. Also, there are a lot of people who stopped using Steemit.
It's hard to know exactly but it's in the tens of thousands. Even now during the bear market. During the bubble we had more than 200 000 daily users.