1. The mode shape will illustrate locations where there is significant deflection. These are good locations for added restraint.

2. Increase the frequency cutoff. You may also address this by increasing precision on the Advanced tab.

3. Your modal results do not show response to the slug. But the restraint configuration considers the slug loads you ran in your static analysis. I would run the modal analysis based on support configuration both with and without the slug just to see if things change much.