You get 1000 gems at player level 5 and, as others have mentioned, 150 gems every 25 levels.
Your hero attacks when they're near something that can be attacked (except walls, idle mercs, idle objectives, or if you're stealthed), when you attack-move on the ground (A+left click), or when you right-click on an enemy.
When Tracer reloads, a blue bar appears on the screen with a slider that moves to the left. If you take the talent (Locked and Loaded?) then a marker gets added on the bar. Press the reload button again when the slider moves past the marker for the damage buff on your next clip. Hope that makes sense.
The correct time to reload manually is anytime you're not shooting/expecting to shoot (rotating, chasing, escaping). Note that Tracer automatically reloads when you mount.
The lane setup is a little less rigid in HotS than other MOBAs. Split sensibly and respond to the enemy team. Generally you want to have a strong solo laner (hero with self-sustain and decent wave clear) in the lane furthest from the other lanes/first objective spawns -- this differs by map.
No one knows.
