Well apparently, I'm wanted on this topic
Okay I agree that having a plan is very important. Know what you want to say and when. You can schedule, however, you need to go back to see what replies are being sent to you, etc. You can't just say things and walk away. Its like talking at someone and hanging up the phone. So while you can use scheduling software, don't depend on it and cross social media off your list as done.
Kimberly is right, its better to provide content that is unique to Facebook and Twitter. However, you can use things both places. Lots of customers are not comfortable with one or the other so you may be reaching different people.
You can schedule things out ahead of time on your planned topic, however, be open to adding things as new stories come up, products come out etc. People want to feel like they are chatting with you.
Attrition is low with social media. Meaning, that if someone "likes" you on Facbeook, you will really have to bother them in order for them to "unlike" you.
Some organizing choose to hire an outside firm, while many do social media themselves. If you are doing it yourself, limit the time you spend. Otherwise you can get sucked in and spend a whole day "social mediaing".