Largely thanks to Joerg's criticism, we have made some major revisions.
POW now functions as a sort of "magical encumbrance" along the lines of free INT rather than as a stock of points. A character who can channel can hold a point total of weaves not exceeding their POW.
Exceeding this limit or channeling for extended periods of time requires a CON roll, beginning at CON x 5 and reducing in multiplicity every time you are forced to make it. Failing this roll means you must let go of the Source and are too tired to channel or to do much of anything; fumbling means rolling on a “channeling fumble table” and can result in unconsciousness, HP loss, explosions, being severed, or other consequences. Results are modified by how much/how long you were overchanneling.
Another constraint is your “multichanneling score.” Although a character can channel points up to their POW, the number of ways they can divide the flows is limited (see Elayne’s first encounter with a Sea Folk Windfinder channeling in The Shadow Rising.) This limit is initially based on INT—1 for 12 and below, 2 for 13-16, 3 for 17 and above—but can be trained up over time.
Angreal and sa’angreal increase channeling capacity, basically serving as extra POW (a static number.) Linking does the same, but we still need to work out a curve for it. Wells give points, rather like magic points, that can be “used up,” each point supplying one POW for one melee round.
For easier bookkeeping, weaves (Joerg, see Chapter 10 in Crossroads of Twilight, p. 316 in the paperback) are grouped into Talents (we were probably just going to steal the d20 ones.) Along with tying off a weave and unraveling one, these make up the skills in a Channeling skill category, with INT and POW both being major modifiers.
We got our information about the d20 game from a 5e conversion PDF we found in this Reddit post.