The best way is to add a table at a time til you find your comfort level, or exceed it is better said. I play w/o HUD on 90% of the time, but have it ready for a quick check if I need it. That way my tables aren't cluttered with the HUD, but that's my preference.
Add a table and if you comfortable, add another. There will be a point that you will play worse, and you don't want to exceed that,obv.
I am bored with less than 4, and good up until 7 tables for cash games. Once I hit 8,unless it's all razz or stud/8, I am not being smart for my game.