For example, what applications are the 50 people using? Are there any other customer facing applications, including websites? How many of the users are active at any one time? Are there specific performance or availability requirements along with how much data exists? In addition to the amount of data, how much does it grow on average year to year? Are there plans to introduce new applications in the future that would require more server compute, I/O, memory or disk storage resources? Also, are you currently using a network-attached storage (NAS) device for Windows CIFS or NFS file serving, or will the server you are looking for need to support file serving for users home directors and file shares?
Depending upon the answers to these questions, you may find yourself with a single server with internal or external storage, or perhaps a pair of servers configured with external shared storage for frequency. Unless your 50 people are high-end power users, and your server also needs to support customer facing applications demanding large amounts of compute power, a blade storage system may not be the best fit.
A more general-purpose server might fit your requirements. Specifically, the server should have enough processing power to meet your needs, as well as the ability to expand for additional or faster processing cores (CPUs), additional memory and I/O expansion capabilities. If you plan on supporting any virtual servers along with databases such as Oracle or Microsoft SQL server (which is also the database for SharePoint), you will want as much fast memory as you can afford. Regarding storage, you might be able to leverage a single server with internal dedicated direct-attached storage (DAS), including a mix of high-performance SAS and high-capacity SATA drives, or, perhaps a shareable external DAS, SAS, RAID array. For backing up the server, one possibility is installing software on the server to back the storage up to an external backup device such as a physical automated tape library. You can also back your server up to a disk-based storage system with data deduplication and optional data replication to an alternative site. Another option is to configure a separate backup server, or, if you install a pair of servers for failover and high availability, utilize one of those as a backup server.
The bottom line is that the right type of server for your needs will depend on your specific requirements, including the budget for your IT department.