you can just disconnect when your not using it
and phone line >> router >> computer is the way to go.
AVG is very good with updates. For virus.
But truefully the most important thing to do is to read an learn. And understand why things happen.
If your going to use a fire wall. Read about it and learn it.
If your going to use adware software read about it.
I would recommend for browsing problems to update your host file to block out adds. Look for someone Online who does this and constantly update your host file. Sites such as this link
http://www.everythingisnt.com/hosts.html
Virus software should be set to update every 6 hours and have it constantly scanning all inbound traffic.
Firewalls are good. If you use them properly.
Learn to read log files and understand them.
Then read up on how to hack a computer.
Start with a nice easy book like Hacking for Dummies.
Learn how to hack and you will learn how to protect.
and follow the advice that sivran gives ..