Hi, The backup utility provided by Realm is available for all editions, take a look at the documentation found here:
Ideally, you would run the manual backup as part of a cron job at regular intervals, the continuous backup feature is limited to our Enterprise Edition.
There is no hard limit on the number of users per ROS but A good rule of thumb we use is around 10000 users per server but this varies based on the number of active connections, the number of times data is changed (synced), and the size of the data transferred (changed). With only 50-200 users active at any one time you could probably go beyond our rule of thumb but you should test for yourself.
We have heard from our community that startup pricing is needed and while we don't have anything yet we do value your feedback, stay tuned! And thanks for using Realm.