I cant decide for you if you should pay for the Pro or Ais versions of avast as this is purely up to you and your preference and other security you might already have installed eg firewall, if you would like the benifit of the extra feature that come in pro or ais then use the trial and see if you like it, for me i only required the free version.
The same pretty much applies to an email client in that the decision is really up to your own requirements, if you want to bring the mail into your system then i recommend Thunderbird but if you've only got the one mail account then for me i would leave it to just checking the mail online.