In Classic, playing different classes actually feels different in more ways than just their abilities, at least if you think about it a little. Playing a priest, you really want to find a group because that's what the class was designed for, which is both good and bad - you're stuck very slowly leveling if you're solo, emphasizing the frustration of the slow pulling, but having different classes require different gameplay can be good. If you want to play a priest you're going to have to be more social by default, just whisper the guy you see killing stuff next to you and go level together, you'll immediately have a better time of it (this part is particularly exacerbated in the beta, as there are fewer players).
Keep in mind that these quests are optional, and are not necessary to continue leveling and capturing companions. They are also account-wide, so if you complete the quest chain on one character, you will not be able to complete it again on another. However, any progress that you've made will be saved and you can pick up where you left off in the quest chain on another character. The dailies that you've unlocked will also be accessible by all your toons.
Simply playing the auction house can be the most lucrative gold making ventures if you have a sizable gold staff and you're not afraid to spend it. Just like a real world stock market, prices of items traded on the Auction House fluctuate daily, creating opportunities to buy low and sell high. Zygor's Gold and Auctions guide finds items that are selling at record lows for you to buy them out!
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
There are two parts of the quest chain for each continent. The first part involves defeating numerous Master Pet Tamers, and the second requires you to triumph over the Grand Master Tamer. After you've bested the Grand Master Tamer, dailies from each Tamer will unlock for that continent. All the dailies continue to reward experience for your companions, however only the Grand Master daily quest will reward the Sack of Pet Supplies.