Setting up an Android device as file server

I have a spare Android device which I always leave at home. I wonder if i can use it as a file server using its mobile hotspot because I don't have a router and internet at home. Friends always come and always ask to share a few MP3s. I'd like them to browse my Android server at their own leisure without deleting anything. I have servers ultimate installed, but it always requires to be connected via router or Wi-Fi. Can't seem to find the option so that it will not require an active net connection.