Before I ever knew trackers even existed, I was regularly doing 4 of Party Pokers freerolls
at a time. That was the comfort spot for the monitor I had at the time. It was also before I found CC.
Once I realized I needed help with my game, I found CC, found out about trackers and HUDs, and increased my win rate to the profitable side of the ledger (if we ignore slave wages).
Trackers, and HUDs (Heads Up Displays) keep track of what is dynamically happening at your table. Player 1 is very active, Player 2 is tight, player 3 is playing the same type game as me, etc etc. This info is available right below a players position on the table, right now, and once you know what it is you have chosen to show, you can act on facts.
Popular trackers (with built in HUDs) today are PokerTracker3, and HEM (HoldEmManager).
Both offer trials for free, HEM may still offer a micro version cheaper than a full blown version. I use PT3 and don't know much about HEM.
As of 2 months ago (approximate guess) PT3 was better for tourneys, while many prefered HEM for ring.
Let me add that the conventional thinking is that multi-tabling is a learnable talent. There are several folks here who can do 20 tables at a time. My comfort zone seems to be 6, but I don't do that very often.
Those who do lots say they worked their ways up to those big numbers. There are rumors of 25+ at a time.