Should I migrate my whole file server to SharePoint as my sole document storage platform?

No, many files are not suitable for storing in a web-based format.

Also, SharePoint's infrastructure and admin costs are far greater than those of a file server. Only migrate documents that benefit from a managed, version-controlled collaborative space.

Identify active and non-active files and keep the non-active files on cheaper storage in file servers. Index them via search and/or plug them seamlessly into the web experience using third-party add-ons.