Yes, your account will still be accessible. Your PSN account's details are all stored online, on Sony's servers.
You can redownload all the content you previously purchased with your PSN account. Just log back in, select Playstation Store in the XMB and then access "My Downloads". It's a list of all the content you own.
Backing up your content is another easier solution. Make sure to delete anything that isn't Sony-approved, including game saves, game data, software, etc. 8GB is probably just enough for your saves and a couple of games.