It's really easy. I used a 17-inch laptop. All you have to do is stack the tables, full screen, right on top of each other. Each one pops up automatically when it is your turn to act. You only have to focus your eyes and attention on one spot. It's not too hard to see what is going on at the table in a couple of seconds (with a HUD).
I could never do it the way I see most people multi-table, where they have little tiny windows all tiled across big monitors, each one blinking at you to do something. I'd go cross-eyed in about 30 seconds.
The way I did it I could easily get in 1,000 hands an hour. But it was very tiring even so. I usually only played for an hour, 2 or 3 times a day. But that could be 3,000 - 5,000 hands a day if I played a bit longer than an hour each time.
Oh, yeah. There was another big advantage I found. You didn't ever have to suffer through bad beats that would make you tilt. You could look at all that afterwards in your database, and by then, you could pretty much laugh them off.