We use Planning Center Online for our Childrens/Youth and Worship ministries. Before starting w/Planning Center Online, I contacted Fellowship Technologies to see if there was an easier way than maintaining 2 databases (the same questions you're asking now). Unfortunately, I was told there was not.
To use F1, we must run a query on each of the 5 service times for each of the ministry areas in our church, then send email reminders to our volunteers. Through Planning Center Online, I simply click "Send", and an email is sent to the volunteers, asking if they will be serving. On Friday, another email is automatically sent, letting the volunteers know they are scheduled...simply "reminding" them one last time that they are scheduled. PCO makes it simple, quick...and is very affordable.
The real "drawback" to using PCO is it's a second database to maintain. If a volunteer changes his email address in PCO, for instance, I have to "catch" it to update F1.
I wish you the best!!!