1. It's important to show your work, if only to make it easier for others to see whether you are doing the right thing. Mere numbers are too anonymous. After calculating, I see that you chose to use permutations; here the problem could have been clearer, as it doesn't explicitly say the 8 officers have distinct offices (as you are assuming), so you are going by cultural expectations rather than what is actually stated. It is conceivable that the "slate of 8 officers" could just be 8 equal leaders, in which case combinations would be appropriate. I suppose you are probably right, but I wish the problem had been explicit, as these usually are.
2. The committee definitely consists of 8 undistinguished positions, so combinations are appropriate. As I read it, the 8 officers have been elected, leaving 16 non-officers, from whom 8 on the committee are to be chosen.