We've been using QuickBooks for close to 20 years for all of our accounting needs. In the past 7 years, we've added the QuickBook Server capability to enhance our Bookkeeping Department and have found it very useful.
2 - QuickBooks is utilized by my Billing Assistant and myself. My Billing Assistant utilizes QuickBooks for invoice entry, vendor entries and credit card transactions. I utilize it for all other accounting processes.
We do not have an internal Support person - basically that person is me. When and if, we cannot do something that I want to do, I speak with my Accountant and his office assists me. If they can't help me, I then contact Support for Quickbooks directly
I've been using the QuickBooks online version for a little over 6 months now (upgraded from Mac desktop) and I haven't had any access issues. There have been times when it was down for service/upgrade however there is always plenty of notification time given by the Quick Books Online Support team. These upgrade maintenance time frames are always over night hours and on the weekends so everything can be worked around very easily.