First yes of course you should enable the firewall as you should enable all updates for security.
Secondly yes you should consider upgrading as win7 is dead as of... er now.
You really really dont want to be running around the internet with only basic or... no protection and a browser as old and crap as that found in early versions of win 7. You just dont although it could be worse and you could have what i found on an epos till last week - XP embedded, no updates, practically no virus checking and the only thing keeping the monsters at bay is a vlan with limited external access....