Question 1: Should the San Antonio Spurs have traded DeRozan?
After opting not to trade DeMar DeRozan each of the last two seasons, it appeared unlikely that the Spurs would receive any value in return for their best player ahead of free agency. However, the Spurs and Bulls were able to come to terms on a sign-and-trade that sent DeRozan to the Bulls in exchange for Young, Amino (who may be waived or traded), a 2025 1st-rounder, a Lakers 2022 2nd, and a Bulls 2025 2nd-round pick. For the Spurs; receiving three picks, including a future first, as well as a solid power forward in Young, is a great return value, especially considering DeMar wasn't going to re-sign.
That said, there are some negatives to the deal. For instance, the sign-and-trade removed the Spurs from contention for restricted free agent John Collins. Furthermore, the deal forced San Antonio to take back Aminu, who is owed $10.4 million next season despite his poor play. Also, after rumored interest in Lauri Markkanen, San Antonio's decision not to try and include him in a double sign and trade in place of Young is questionable.
Perhaps part of the reason the Spurs agreed to the deal was to do DeMar a favor after three impressive seasons. After all, he was able to pick his destination and received a new $85 million contract, something that another team couldn't have given him.
Another reason could be that the Spurs expected Collins to re-sign with Atlanta, thus leaving the team with nearly $30 million in cap with no one to spend it on. However, they could have conceivably signed both Markkanen and Kelly Oubre Jr. had they decided against the trade.