Home Network Design with NAS

I’m looking for advice on how to architect my home network but I’m confused on how to accomplish what I want. Here’s what I have today:

2 Macbook pros
2 ipads
2 iphones
1 windows PC
1 500gig Time Capsule

Here are my requirements:

1. Have NAS storage to put pictures and other share data on (1TB min)
   
2. Has to allow the windows machine access to it.
   
3. The NAS has to also be backed up on another device so I’m not betting the farm on one hardware device.
   
4. Run time machine to backup the Mac’s.

How would you put this together?

Thanks in advance!