Hi Polly!
To answer your questions about d ratings, when you initially draft a player, his real life +/- ratings mean nothing. The sim bases the player based on the rating he was assigned. There has been much discussion on this previously, as Dan Hamhuis and his 99 d rating will show. Anyone who knows hockey knows that in no way, shape, or form was he the best defensive defenseman to ever play the game, regardless of his WIS rating. Also, you will notice how few owners will use some of the all-time great players to ever play the game (Howe, Richard, Bathgate, etc..) as most of those players had stats that did not translate well to the "modern day" NHL. Much debate about that has gone on in the past as well. Regardless, games played, shooting % and shots per game, pim per game, d rating, and to a lesser extent assists per game is what you want to look for when drafting a player. All of that is taken into consideration when WIS assigns a salary to a player.
As far as user settings go, aggressive is a sure way to lose. I occasionally use aggressive on my power play, and sometimes (depending on my opponent) in the last minute of the game. The best way to figure out settings is to experiment with them in ten game cycles. See how your team performs against your opponents, but keep in mind if you play weaker teams the results may be skewered slightly. Most players though use a mix of conservative and checking, with some medium thrown in.
This is the WIS description: https://www.whatifsports.com/knowledgebase/KB_Article_Details.aspx?kbid=192
As you may have noticed, there are some advanced settings in the Coach's Office that will allow you to set a specific style based on certain criteria. The "Default Offensive Style" is the style the line plays if none of your advanced criteria is met. Aggressive means that your line will play an aggressive forecheck, increasing your likelihood of scoring but at also increases the chances of your opponent scoring on you. Medium means that your line will not be as aggressive and your defense will be more solid as well. Conservative means that your line will focus on defense and not try hard to score goals. Checking means your line will play a more physical game, hitting harder. The effects are that the line focuses less on offense and more on playing defense and getting turnovers. The checking style can also fatigue the opponents (in-game) slightly more, but also makes your line slightly more likely to commit penalties since they are playing more physically.
Hope that helps to answer your question!