I have few generic questions about firewalls and I thought the community up here could help me out.

1) So I recently installed Ubuntu server barebones. I checked for open ports, none were open which was great. Is that because there was a firewall installed or was it because there were no applications installed?

2) I installed some applications, (Apache, postgres,ssh, Java app and some few). Between these, I ended up opening a few ports (~10). Now I have a list of all the ports I would need open. So, how do I go about protecting them? [Is this the right question to ask? does the process go like this, Install Firewall -> Allow Said needed ports -> deny rest using IPtables rules]

This is going to be open to the internet. Hosting low traffic ecommerce sites.

3) What do you think is the easiest way for me to quasi-secure the server, [low maintenance overhead/simplicity. Any open source "software" which can make my life easier?]

4) Finally, of the said open ports [2], I have 2 ports I need to close because they are telnet ports. Can I close these ports without installing a "firewall"

Thanks all for the help and Merry Christmas!!!!!!!