If you looking to set firewall rules to the internet, sure dd-wrt can do that. If your looking to setup firewall rules from clients on your network to your nas. Unless you setup vlans or multiple network segments. Which you can do in dd-wrt, you would not be able to setup firewall rules for clients to other clients on the same network.
local network traffic does not go through the router, it would have to be something off the local network - like internet or another network segment to firewall.
Unless your talking about wireless clients talking to other wireless clients with is called AP isolation or client isolation.
There is no gui that I am aware of for doing firewall rules between network segments. But you can do pretty much anything you want from the cmdline with iptables directly.
yes you can create host entries so for example nas.local.lan would resolve to your nas IP. This can be done very simple if the nas is dhcp.. Or if you set it up static and not just a reservation then sure you can create entries so they will resolve. But again I don't think there is gui for this sort of optionhttp://www.dd-wrt.co...network_-_HOWTO
If your really looking for networking features like full blown dhcp servers and dns, etc. You might be better off just using a firewall/router distro like pfsense, ipcop, m0n0wall, smoothwall, etc. Just use your current wireless router as the accesspoint and control the other aspects of your network with true router/firewall distro.
This will for one give you nice easy gui to work with vs cmdline iptable commands
example here is firewall interface on pfsense. This is my wireless segment wlan, I allow my ipad to go anywhere and access anything on my lan or dmz segments, etc. But other wireless devices are denied other than talking to the printer on 192.168.1.50 or the ntp server at 192.168.1.40. The last rule says that you can go anywhere you want as long as its not the lan network
If you want you can run full blown BIND as a package, but the dnsmasq built in allows for easy creation of dns hosts, etc.
While 3rd party can add loads and loads of features and fixes to wireless router hardware, and make them very useful and productive leaps and bounds above the native firmware. Doing some of the fancy stuff does require cmdline understanding and use.
To be honest though if you want to play with some fancy features, and like the gui. Something like pfsense is way easier to do these sorts of advanced features with
Do you have an old desktop collecting dust? Can you add a 2nd nic to it? Do you have something you can run VMs on - you can run this software as your router in a VM which is what I do on a esxi host.
If you just want to get your feet wet, then 3rd party like dd-wrt, openwrt, tomato, etc. etc. Are great - I am not sure tomato supports netgear though. But it is a bit easier to use, and great feature set.. I would rank them in ease of use tomato, dd-wrt and then openwrt - and same for power of features from left to right.
More than happy to help guide you on your way to discovery of life beyond the crapware the soho router makers push off on their userbase. And then stop development on as soon as their next model comes out, etc.