For point 1: While it's important to hire more as you expand, having too many employees can drain your funds, even more as they level up. Check to see which ones you don't need anymore and fire them and/or replace them with robots (If they're janitors or security guards)
For point 2: As you level up your staff, they gain skill slots, however training them will increase their pay requirements. Sometimes it's okay to leave them empty or leave some of them at rank 1 or 2 since they're sufficient enough as it is.
For point 3: Loyal is super important if you're going for the long run. Lower pay requirements can help relieve the pressure from giving them a pay raise.
For point 4: Skills like Eloquent can improve your staff's skills and Photographic Memory can give you a little boost in getting survey levels up. However some positive traits are not created equal and not all negative traits are a huge threat. Delicate is okay to have as long as you're not sending them out on expeditions or are taking the necessary precautions or willing to wait longer for recovery.