It depends oh how big is your app. As a standard if you want to show the tabs i would not exceed more than 6 (personally). If i need more tabs i would use Hide show sheets and give some navigation buttons to the users by hiding the tabs. I worked a DB which has more than 10 tabs, i used textobjects with action to hide show sheets with drop down menu kind of.
I have over 1000 tables and other objects and have never been limited to create new tables, of course your server or computer has to have enough memory and processor to handle the application.
