In the beginning of battle with Trollocs in KoD, Rand was spinning 12 webs simultaneously: 6 Blossoms of Fire and 6 Deathgates. Than he started spinning 10 webs of Arrows of Fire from his 10 fingers.

But there is one interesting quote:
"Suddenly there was a Myrddraal afoot beside the window, pale eyeless face as calm as an Aes Sedai's black sword already stabbing toward him. Two thrown Aiel spears took it in the chest, and a throwing knife blossomed in its throat, but it only staggered before resuming the thrust. Rand bunched his fingers together, and just before the blade reached him, a hundred Arrows of Fire ripped through the Myrddraal, flinging it back twenty paces to lie riddled and leaking black blood onto the ground."

So, in the tense moment, LTT was able to spun 100 webs simultaneously.