1- at d3 I will start thinking about a + at 70. For d2 it's probably closer to 75. If a kid has good ath and spd and can create attempts then I might go lower. It partly depends how well he can score in other ways, but that is a cliff notes ballpark.
2- absolutely not. Play to your strengths and if the arc isn't one of them then why risk it? I won't put all my guys at -2 the way I have seen some coaches, but I have gone -1 almost across the board with my posts at -2 in the past. If a guy wants to go a big minus, let him. If I cannot win then that's on me for not recruiting enough balance.