12 was easy for me for years, 6 per each screen. sometimes played 16. Hard to play more, need to change the setup.
It's easy to learn it, and it will help in your other activities.
You need to improve 2 things:
1) your APM (actions per minute) - by installing APM counter and clicking-clicking mouse and keyboard buttons during many hours to start feeling comfort at 120+ APM
2) practice at 12 free tables for 1 month if you want to play 9 tables for cash in the future... or practice 9 free tables if you want to play 6, or practice 15 for 12. It might be hard to play 12 free tables for start, but body is getting used with time and brain adapts. When you'll be comfortable with your decisions at 12 free tables - you can try to play 6-9 tables for min cash or lowest buy-in SnGs/MTTs. You will find it boring when you're stepping down from 12 to 6 tables...
and ofc, you need a good setup. one large and one or several additional screens needed, minimal setup is laptop + 24-32" screen or more. Monitor of the laptop for lobby, and other monitors for the tables.. Keyboard shortcuts for bets is a must have, mouse with 5-7 buttons, binding and using most of these buttons is another must have. 12 tables is actually easy. I don't know, maybe I could play more tables with comfort at just one big screen, haven't tried it in past, and not going to try this in the future, enough for me.
P.S. In the past, like 20 years ago, when I was young, I was playing StarCraft at the battleNET and was in top 100 several times, played against Elky and other top 10 players in the world, that's where I've learned to click
)) the best Strcraft player in the world - Slayers_boxer had APM above 320... that's more than 5 actions per second, and such actions are not like typing. It's something out of this planet.... It's hard to explain, and games are different today, Starcraft was like chess compared to todays games for dummies.Elky was the reason why I've paid interest to online poker and started to study it
By the way - Enjoy the video, his setup is nice.