Ask HN: How to Build an In-Office Server

Any advice for building a office server* for a small company (10 people)? Main use would be backups of files vital to our business but hope to setup redundancies as well. Also cannot complain to run internal intensive computation test. Any stories, obstacles, things not to overlook would be appreciated.

*I know there may be some thoughts on the waste, resources, needed for in house server compared to cloud but we need/obligated to have an in-office server for backups in general. We do have cloud services.