That is not a software but it's the router page for Asus. Looks nice right?
Actually you can still monitor your router given by TM. I only know DIR615. You can check under LAN Setup page, you can see how many user is connected to your router and the IP/Mac Address/Name of the computer. Before that, you must identify the MAC address of all your wireless devices only then you know which one is urs and which one is unknown client. Before that, please change your router login page password as if you're still using default password for router login page, those with Little Knowledge in this know how exactly they can change your setting and probably disallow you to enter the router page. After that, you can choose to allow ONLY the Mac Addresses of your Wireless devices to access the Wifi but doing this, you'll need to add MAC address of new wireless device you have in your hand before these devices can connect to the router. Besides that, you can choose just to block MAC Addresses that you don't know who they are and change Wireless Key again after that. (This step is for the case where ppl will say changing the MAC Address of a Laptop/PC is not hard, blocking MAC Address is useless or whatever because as long as they change their MAC Address, they will be able to connect to your router again. So, change the Wireless Password when unknown device is detected in your wifi). Lastly, your wireless better not to use WEP. Use WPA/WPA2 with PSK which is secure enough and hard enough to be break in.
May you refer www.klseet.com for replacement options. I don't think your usage is considered heavy. The thing is that you might need a router with bandwidth allocation/priority feature to prioritize your game packets before any other packets. The last one shouldn't be hard in TP-Link (I don't have asus...) because in TP-Link, you can set exactly the maximum and minimum egress and ingress bandwidth that a particular device can use. Tested to be working. You can just give 2M out of 5M for her or something like that. P2P wise, you need to cap it on your computer. If you're leaving 3M for yourselves, probably cap it to 2M or 2.5M. Also, limit the number of connections for P2P. NAS shouldn't be a problem for all those routers except if you want to use USB attached NAS then it's different case. You need a USB port for that. Asus routers with USB supports BT client IN THE ROUTER, directly to External Harddisk connected to its USB Port. Tried TP-link 1043ND emulator, even though it has USB port but default firmware doesn't have much to play. Try it here: http://www.tp-link.com/resources/simulator...043ND/index.htm

Asus has traffic priority feature, asus name it "EZQoS - Quality of Service" but how well it works? Ask those using it. I don't have one.
Found the simulator of N16. Play with it yourselves and see whether it suits you: http://event.asus.com/2009/networks/dummy_...-n16/EZQoS.html
Your question is far too general. no idea how to answer ==

Must be FTTH. Rite ?

most user says stock router dir615 are cheap & crap. earlier usage ok la but then after a period of time, speed become less, wifi signal not strong, easily kong etc. tm ppl can replace faulty dir615 but still happen as they replace the exact same model. that's why ppl like klseet & rizvan do r n d and give us alternative to buy router  other than stock model that can be used for unifi customer, which is better than stock

even im afraid that when they come to install unifi at my house this saturday, i have to prepare some $$$ to buy a backup alternatif router

correct me if im wrong