Linksys Router Stack

I have a stack of Linksys routers, namely; BEFSR41V3, BEFSR81, and the new WRTN300. I have the WRTN300 as my gateway router, the 8 port has my fileserver 3 port Fileserver NIC connected to it, and the 4 port is just there for other user computers. I added some height to the legs because of heat, and a fan to the top router as well as one on the side to draw heat away. I even added a fan on top of my cable modem cause I was bored, all powered off an old power supply. I am new to wireless networking and was wondering if anyone had tips to get the most out of my new router, any security issues I should know about, and any cool mods I could do without opening the routers up. I have an old befsr41v1 I opened cause it was so old, it's just sitting in my drawer sleepin till I have a use for it now.