you can only have 5 at any one time, however this is why the save overview feature exists. with that you can load any of your saved overviews into a tab so when i'm not in fleet ops i have a default, a mining, a mission and a basic "PvP" just in case, then in fleet mode i different sets depending on the ship i'm flying
I'm yet to work out how to save one so it doesn't end up as the default. I failed on numerous occasions when I attempted this on my old char and haven't tried on the new one yet. I have one tab.