This question looks the same as the one you asked 8 months ago, but I'll try to answer:
In answer to your questions, yes, a daily backup is created, you have a limitation of 100MB data storage and 100MB file storage. You can add users, it's up to you how you configure your project. Obviously you have other limitations as well, the app goes to sleep after an hour so it will take some time to go up. It has a limitation of 10 internal users. You have no official support, only from community etc.
Also check FAQ.
And some info from a free app the following info from the sprintr:
I have developed a tool in Mendix that offers all you need: Crm, messaging, workflow, document management, task management, project management and calendar and some other features. It's all-in, has a fee per month per user and I will configure it for you as you like it. It works for me since 2 years and is ready for other companies. You could start using it tomorrow because it is already generally avaiable, however no real marketing going on yet. If you are interested please mail me at email@example.com and we'll get in touch. You can even use it to connect with customers and peers.
Just to expand on Corne's answer regarding this particular point.
limitation of 10 internal users
It is not 100% clear in the docs, but from my understanding this refers to the number of concurrent users. So at any point in time you can only have 10 people logged in to the app. If everyone is careful to log out after they are finished with the app this should not be such a big issue.
However there is another limitations: 100 user account. Basically, you can only have up to 100 user accounts with login credentials. Since you probably want to make sure that only authorised people can use your app this is something to consider.