Selling stuff is pretty simple. You put stuff from either your inventory or your retainer's up for a price. People can see that price and choose to buy the item(s) or not. If you're selling stacks, they can only buy exactly what you've put up; so it's a good idea to have some idea of the quantities people need of some items. E.g., if you've got 7 of something, it might sell faster as a stack of 5 and 2 individual items than as a stack of 7. And you can generally charge a little more per item for smaller stacks, since people will often buy only what they need. When you go to set the price, there is a little page icon in the upper right of that window that shows the sales history for that item.
For shouts and yells, just be reasonable. Everyone has a different threshold for annoyance, and it also depends on how much else is being shouted/yelled, and how long the thing you're shouting is. "LFM 2xTank Coil T6" only takes up one line and doesn't interfere with other chat too badly. A giant FC recruitment shout that takes up four lines gets in the way and should be throttled a little more.
1. Better than what? You can pick up a gathering class for easy gil. Take the allagan pieces for all your quest rewards. Find stuff on the market boards that's being sold for less than its vendor price. Do leves and/or FATEs. Find stuff you can buy at vendors and sell on the boards for a profit (Y'know, like selling Distilled Water for hundreds apiece on the Jueno AH).
2. Why on earth do you need that much for level 1-10? Stay away from the market board, buy stuff off vendors or get it from quests or just don't bother upgrading anything other than your weapon and offhand (where applicable) because the starting gear is enough up to level 10. You'll want some better gear for dungeons at level 15, but again, vendors.
Edit: Really, early on, it's more about how much you save than how much you make. Look for ways to cut your expenses. Walk when you can stand to. Use Chocobo porters instead of teleports. Check both vendors and the market boards for anything you're thinking about buying; either one might be cheaper depending on what you're after. http://xivdb.com is great for looking up vendor prices and locations. If you've got an FC or LS, it doesn't hurt to check if someone can craft you something for cheap.
3. There's no way to change your name.