in one of my leagues, I've sealed my spot in the playoffs.

does resting my starters (5-10 minutes less) during the remaining games of the regular season affect how many minutes i can give them in the playoffs? or does it just reset the minutes allotment? as in, after resting them, can i play my players 3-5 minutes more than they're supposed to?

You can use your players for up to 102% of their minutes without fatigue during the regular season.  If you do not use the entire 102% of a player's minutes but 100% or less, I think you get a bonus on how many minutes you can use a player during the playoffs.  I think you get 1/4 of the unused extra 2%, but I have not been able to determine if this is correct. 

I am not certain about any of this.  Experiment with things and let me know what you find out. 

I am not sure what happens if you use more than a players 102%, but I will find out soon.  I do not think that there is any carryover for minutes below the 100% threshold.  I think that if you use 98% of a player's "bonus" you will get the same benefit as if you used 100% of their minutes.

Somebody can correct me on this if they feel this information is wrong, and, please do.

Fatigue resets for the playoffs.  The exception is overused players... If you have guys at 95% or lower fatigue, then yeah, resting them would be a good idea.  But you don't get any bonus over the normal 102%.

However, if you have a 1st round bye, then yes, you get a big bonus to fatigue as you'll have at least four games to "store up" fatigue.  It's a terribly unfair advantage that a good team under a good owner will almost always use to their advantage.