Each battle that you win will yield experience for each pet that participated. However, deceased companions will not receive any experience (so make an effort to keep them alive by swaping in a different pet). Experience gains are based on your pet's level compared to the wild pet. Defeating a higher level opponent will grant more experience than a much lower level one, but be ready for a tough fight!
You will need initial funds to start this way. Buy for cheap and sell for actual price or higher – that sounds pretty easy. But you should have basic knowledge of prices and always track the market. People use to sell for cheap when they need fast gold or don’t know real value of the item. So, it’s your chance to act. If you see anyone selling an item for low price in trade channel, contact them immediately. You should use all of your trade skills to negotiate about the price to make it as low as possible. It’s important ability to communicate. Besides, it’s good to get addons to trade effectively on Auction House: Aux or Auctioneer. They allow you to scan auction, compare prices, find cheapest options, post items quickly, and many other useful tools. It is possible to make your first thousand out of ten gold you have in a pocket.
An advice for those who are trying to compete monopolizers: you cannot beat them by selling for less if they follow right steps. You should do opposite: sell for more. Because market will come down if the price goes unreasonably high. You can set a bid on item for the price it should cost and buy out price for higher than a monopolizer is selling. So, common buyer may get an item for the right price or monopolizer has to buy the item at his loss.
And for talent builds. I prefer to make my own talent builds. But I've been playing RPGs since the 8bit days so half the fun is building my own characters up. I already made and bookmarked 1 deep fire mage build, 2 elemental mage builds, and 2 deep frost mage builds. And I might remake them tomorrow if I read up on any good talent choices I left out my 1st 5 times lol. And I have multiple builds for the other classes I play too.