The metagame does change from time to time, but usually you can key in on how frequent players play and what cards they like to use. Just like in Magic. There are some cards that do become permanent fixtures with some of the players (Zeromn, Rouetsoleil, Red Cap, Goblin's Lair, etc.), but not everyone.
There aren't any banned cards typically, although I've heard rumors of some people setting up the game rules so that no Fire cards could be played.
Many players, like the tournament regulars and ladder players on this site choose to not play with or against E cards. These players will set up the rules for no E cards.
It sort of just depends on the players though. If you have a mic, just ask the opponent their feelings about E cards if you have a strong feeling regarding E cards (one way or the other). You can always send a quick message too. Most people need 5 minutes or so to tweak decks at the beginning, so there is no issue if you need a little time.
I'd recommend getting a bunch of cards first before you start online, if you haven't already. It is WAY different from playing the AI. Here is a link to a card farming method that you can use solo for your reference.
http://www.culdceptcentral.com/index.php?option=com_content&view=article&id=288&Itemid=210
These are just some of my thoughts on your questions / issues below. Glad you are having fun with the game!