FreeNAS is not appropriate in your use case. I do not see any reason that FreeNAS is the right choice for you here.
You are using only one disk (this removes the ability to protect your data as there is no redundancy), which is the biggest benefit to using FreeNAS. The overhead associated with running FreeNAS is much greater than just about any other solution out there, for such a simple set up.
There are other options for a NAS software with web based management:
NAS4FREE
OpenMediaVault
UNRaid
RockStor
Zentyal
just to name a few