(2) Consider whether the letter adds something that's not already in your packet. Letters from another teacher or someone who knows you from school aren't likely to add anything extra or help. Letters from an employer, a pastor, or someone else who knows you outside of school MIGHT help
Very true.
Our DS athletically did TKD. He was a state and national champ. However, he did not play any "traditional" sports. We had the Master(he was the Olympic Gold Medalist for SKorea back in the 90's, and signed it that way under his name) send a letter explaining that participating in competitive TKD, requires at least 20 hrs a week YR ROUND. That this would be similar to playing 3 different sports because there is no break. Additionally, that he competed on the State and National level for 3 yrs, where he was always the Gold medalist in States, and never lower then the Bronze in Nationals.
We also sent an additional letter from his employer, for basically the same reason. Our DS was a SR Lifeguard for 2 yrs, (yr round). In that letter, the director of the Y, spelled out not only his duties as the SR Lifeguard, which included training jr lifeguards, but explained that as a SR guard he was required to be tested monthly in certain swimming skills, including rescuing a 140 lb dummy from the water, and exiting the pool without stairs within 1 minute. She also told them to his credit he had 26 saves.
These are things that can help, because it filled in the holes, that although he was not in school athletics, he had for yrs been very competitive in non-traditional athletics. Those two letters showed that at times he actually spent 40 hrs+ a week in athletic situations for an extended amount of yrs.
I would not rec a letter from your boss if you are working at Target, because what are they really going to say? He/She is prompt and courteous? That doesn't help.
A Pastor or church leader maybe different, but I would stress that you only ask them if you have done something really unique within the church. For example, you created CYO or Clothes drive. It has to be something shining. Eucharistic minister, CYO treasurer and teaching RE is not a WOW factor.
Whatever letters you decide to add should be WOW factors. Like USNA stated, they can read it for what it really is worth. They have seen many additional recs, and that is why they know if it is a waste of their time, or something they should give extra attention to. You don't get bonus points because you have more recs. that are BS.