Question #3: How do ratings fluctuate in the game and when do you begin to really get a feel for true ratings?
Actually two very different questions.
Ratings wander slightly (on the underlying 1-250 scale used by the game, and visible in the player editor) regardless. Whether you see this reflected in scout ratings is just luck; sometimes it crosses the threshhold from a rating of 8 to 9, but sometimes not. It does mean, though, that if your .300 hitter is hitting .280 this year, it might be a change in ability and not just statistical noise, even though his visible ratings are unchanged.
But big jumps and falls are also possible, and this is much, much more likely early in a player's career -- especially the first two years, and lasting til the player is about 25. So, if a high draftee turns out to be a bust, you r cannot be certain whether the player had great potential on draft day and then lost it, or whether your scout was wrong in the first place. However, between actual gain/loss of potential and scout's improving on his initial evaluation, the numbers scouts give you early in a player's career can be very volatile.
Current ratings generally follow the potential ratings until the player is 26, then fall below potential ratings later on as age takes its toll. Huge differences in when this occurs, but you can generally count on your stars to fade around age 28, while your rivals hold their skills until about age 40.
One other thing. It's not uncommon for a batter to see an upwards bump in batting eye a little later in his career, and the same is true for pitchers' control.
As to getting a feel for true ratings... I guess for a player who has competed in the majors for a while, scout ratings are pretty much accurate. Before then, it's like real life. If the scout says the guy is one way and that's how the player performs, you can feel reasonably certain. If there is a discrepancy, you are left wondering. I'd say it is very realistic.
When you are talking about prospects, you can do some double checking by looking at the list of top prospects on your team and top prospects in the league. They say these lists are highly accurate as of the date they come (start of the season). The positional strength report gives some further evidence for both major and minor league players.