Thoughts on a NAS.

Sometime in the near future I maybe back underway, and was already thinking of some of the things that I would like to have with me out to sea.  One of the first things that came to mind was some sort of storage device for movies, tv shows, pictures, and games.  

I currently have a 2TB drive that I have been using for quite some time but that is at max capacity. Thinking of picking up another 2TB or 3TB depending on prices but that would be another external device to have.  I would like something that would be able to store about 3-4 drives and that is not to big.

I was thinking about just purchasing a standard NAS but that would take all the fun out of it.  Plus I have some other requirements that would like to be met.  For one it cannot be very big in size.  I don't want it to be the size of a regular PC, as there are not many places to store something like this.  It also has to be easy to secure. When the sea gets rough I want to make sure its held tight (not to big of an issue).  I am not going to go crazy and get SSD drives for this setup (which would be better, but not cost effective for what I would like it to do).

Another issue is that I would like it to be accessible via wireless N by at least 10 user's at a time.  By any sort of devices (Laptops/Computers/Tablets).  But it only needs to serve about living room size area (dont have actual size just yet)  All depends on were I could store this, and have a place to connect the power).

Would also like to set it up to have different levels of access, so I could see everything on there, but others might only see movies, or TV shows.

This will probably be a home build but need help just getting the idea of the ground.  I still have at least a few months to figure this out but wanted to see if anyone could provide me with a starting point, and maybe a price range to look at.  I would be looking at it without the hard drives for the moment.

I will have to get someone to take some measurements so I have an idea of what sizes I would need but I will be going from something the size of the traditional NAS sizes by NETGEAR, DLINK, ect.