Hi, I would let it grow either unchecked to fatten the trunk, then chop it, or let it grow to a reasonable ht. and chop it, either one repeatedly til you have a decent sized trunk plus some twiggy branching. Or you could do a literati and damn the trunk, or you could use Salix babylonica (Weeping w.) and use little weights tied to branch ends to encourage the weeping.

What about S. matsudana 'Totuosa'?

What about it? It has fantastic bark, though how old it needs to be to look like that might matter, but if you mean is the growth habit different from other willows, I don't know, but I wouldn't imagine it's particular so. It's really your call as to what to do with it, or any other tree, as long as you understand its basic needs and probable future.

Wouldn't the contourted stems and wavy trunk make a good informal?

Absolutely. Love them. Good luck with it.

I took three cuttings yesterday of weeping, corkscrew/dragonclaw, and some other upright variety.

What ever happened to this project? Did anyone end up with a successful willow bonsai?