Welcome to Gaia!
I've been here a few years so I can point you around a bit, but I was absent for a time so there are still new things that I am discovering.
Some answers!
1. An excellent way to make gold is to start up and maintain your aquarium. An NPC in that area will tell you how to add fish, feed them, and how to play a game called Booty Grab.
Every few hours certain fish or creatures in your tank will glow, other Gaians who visit your tank will be able to "play" your tank which earns both the player and you essentially free gold. A guide in the Gaia Aquariums section will tell you how to make a Glow Bump thread, and there you can let people know when your tank is glowing and you will get visitors.
This exchange goes two ways; you can also visit tanks and play for gold.
2. This has been sufficiently answered, I think. Tektek.org offers profile code options and it is also an item database that lets you view items you don't own on your avatar.
3. Always make sure you are certain you are posting on the correct board when starting a thread. The directory is large and a bit confusing, and sometimes it takes a bit of digging to find exactly the right board. There are no dire consequences for posting in the wrong place every once in a while, a moderator will move your thread to the correct area. Just don't be a repeat offender~
Some people will try to get into arguments with you, or raise your ire, or generally try to bother you. You are absolutely under no circumstances required to respond to these people, and it is best if you don't. Getting into fights on the internet isn't fun or cool and it can easily be avoided. If you feel it is necessary you may use the ignore function. You can add people to your ignore list by clicking the drop-down under a user's avatar in the forums.
Sometimes folks aren't trying to cause mischief, they're just extra picky about the words you use and how you express ideas. Get ready to spend lots of time formulating your opinions and writing posts. Try to identify unclear language before you hit submit.
I've laid this on pretty thick, but it's a crazy world in here and really no amount of welcome babble will prepare you for the experience you're about to have.
Good luck!