It depends on many reasons. For example, technically is possible because you can create more databases for My Site contents. Each Content Database has a limit for mysite Site Collections (7500 SC). for 46000 users you will need 7 Content DBs.
There aren't any phisical barrier. Just take into account that the more servers you need the more money you have to spend and more management resources.
Regarding the licensing fees, depends on what you negotiate with Microsoft, the version of SharePoint (Foundation
to have an idea of what you need. Keep in mind that the single standard license per server is about $7000.