The first lesson I ever learned in networking was "never ever, ever use an ISP supplied appliance -Take it out the back, have a bonfire or flog it on flea-bay, but whatever you do, don't use it". - - - it's a lesson that has served me well over the years.
In getting that box, you have taken a big step forward IMHO. To learn about how things connect is not only interesting, but you are reclaiming ownership and management of your LAN and anything connected to it for yourself. So high kudos to you. Be prepared to make some mistakes along the way, and be prepared to learn from them.
If your new box is working well today, take a backup of it's settings. Then make one change at a time, and test it. If it all (or parts) goes south on you, then restore from your backup, and then try something else.
First thing I would do, is change your DNS resolver entries. Personally I would recommend using Open-NIC or Open-DNS., (or even Google DNS at a push) - - - By the way, lesson number two was " never ever use an ISP's DNS service"