I think you're making this too complicated for a home network.
I'd pick up something like the
ASUS RT-N66U and flash it with DD-WRT. If you're really that concerned about security, put the wireless in a separate VLAN. Otherwise just use WPA2 personal, don't broadcast the SSID, and use MAC filtering.
From there use a basic gigabit switch with enough additional ports to connect everything. The only feature I'd be concerned about is jumbo frames.
Putting 4 NICs in your server is useless. Are you going to load it with a high end raid controller (expensive) or a bunch of fast SSDs (also expensive)? You would also need fast disks in all your PCs. If not you won't saturate all the NICs anyway. If you're only streaming some movies and moving files about all you will need is a single gigabit NIC.
If you want to use link aggregation, basically teaming 2 NICs together, you will at least need a "smart" switch or a managed switch to support this. Again, I really don't think you will need it.
If you have access to Server 2012, you could set up a domain. Each PC would be joined to the domain. Each user would have their own account. You can set up permissions to deny or allow users access to the files.
I'd start simple if I were you and go from there. If you just have a basic modem (it doesn't do NAT or any routing) you will need to plug the modem into the router, then the router into your switch.