With regards to the wathi doll, we don't know whether the soul needed to power it is of the Few or not, so it is entirely possible that its complex input require a soul for power.
You mean the soul of the person utilizing the wathi doll, correct? You're saying that in addition to the fact that only one of the few can issue a command to the wathi doll, one of the few might be required to provide it with a power source? Sorry, I just want to make sure I'm reading you right.
It's possible, but I think the evidence suggests that once activated the wathi doll can operate without a external magical power source.
Akka activates the wathi doll when he is in the agonic circle which interrupts sorcery. Whenever he tries to cast a spell the circle zaps him, interrupting the process of the casting. He manages to get quick spell out to activate the wathi doll and give a command and then the agonic circle zaps him preventing him from doing any more magic. The wathi doll than continues to act despite the fact that Akka has been zapped. I think that is the wathi doll was relying on Akka as a source of energy than the agonic circles effects would have severed the tie but I could be wrong because their is a big difference between casting a spell and maintaining it.
I can only think of two times that we are given explicit descriptions of the specific exertion that is required to maintain a casting, both of which happen with the scalpoi in the nonmen mansion. Mimara describes the weight of the flashlight-ball on her mind, and Akka describes the weight of the bar of heaven on his mind. Heres how Akka describes it:
The Bar of Heaven had burned for quite some time; Achamian could feel the picking toll of maintaining its meaning in the nethers of his soul—like holding a sum in thought for a span of hours
So maintaining a spell requires a certain metal exertion. It's a far cry from casting a spell which requires the mage to process layers of complicated semantics but it is still appears to be a distinct exertion of concentration.
My guess would be that the agonic circle's zap would interrupt that concentration. I guess it's possible that the circle only interrupts the complex mental gymnastics of an actual cant, and not the much lesser exertion required to maintain a spell but I doubt it.
In any case, I don't see why the wathi doll would require energy from a mage. It's definitely possible to create artifacts that don't require constant energy input. Many of them act without a mage as an energy source. Whores shells, the barriers, chorae (ooh that's another example of a magical artifact that works for the non-few for answer to your first question)
