Sage can handle up to 40 users and I would suggest using Real Time Posting vs Smart Posting.  Some of my clients have had issues with Smart Posting, it is a service and that is just one more thing running in the back ground and Real Time works just as well.  If you are looking for better performance I would suggest trying to host your Sage out on a cloud server.  It is easier to maintain, Sage is faster and there are less touch points and thus less potential issues.  When on a remote server the user goes to Sage vs Sage lobbing the data all around the network.  I have a number of clients with 20+ users that have made this transition and it has really helped them.  Reach out if you want more info.  [email protected]