If you connect your routers internet port or WAN port to the line that goes out to the internet and you place all of your devices on the LAN (internal ports) or even a wireless LAN behind the router, you should be safe as long as you stick to an encrypted Wi-Fi connection, if you decide to go wireless.
The router is your hardware firewall, as long as you keep your devices connected to the LAN side of the router and don't DMZ them, they will be safe. I don't know if you want to send a Wi-Fi signal a long distance but a company called Ubiquiti makes some great long range access points, no need to use power line Ethernet, it is slow and from what I have read, it has many draw backs to it. Ubiquiti website
If you want to confirm you are on your own LAN, turn on file and print sharing and allow the necessary ports to open in the software firewall. If you don't see any unknown PCs that aren't yours in your network, that should confirm you are on your own LAN. You can also download a program called netscan.exe from this website Netscan download site. With this tool you can set the IP range of your network and scan to see, what other devices are found on it. You should only see your won devices
I hope this helps out