A basic bonsai development formula appears to be allow the trunk to grow to desired thickness, cut to 1/3 of the anticipated size of tree and grow a new leader. The maples I have that should be ready for their first chop this spring are stick straight, aside from the angle at which they grow out of the ground. I assume that in order to introduce movement lower down on the trunk I would need to cut lower down on the trunk - lower than 1/3 of the size of the tree. Is it better to trunk chop when the trunk is much smaller to introduce movement early on and allow the tree to grow wild to build the trunk size, or first let it grow to the desired thickness and only then cut down lower than 1/3? Does this make a difference in the speed of development, scar healing, type of movement introduced, etc.?
Introduction of movement can be by chopping and growing a new leader with change of direction or it can be by wiring young growth in a change of direction. So it does not necessarily mean a low chop in Bonsai development.
Taper can be introduced by chop with growing new leader, or selecting branch to replace the trunk, this also introduces a change of direction.
Proportion is where the formulae changes. It will depend on the overall size of the finished tree.
When you are quoting fractions it is easily misinterpreted unless stated with a high degree of specificity.
Do you mean 1/3 distance of overall trunk to the first branch? or do you mean introducing movement at that point?
It is probably best to understand that the best process or formulae will fit the style of development and not be a standard approach for bonsai development.
For example you first sentence might apply for a broom style, however in many other styles introducing movement and taper would be best done lower than that. It is often stated that movement should be introduced as low to the base as possible and taper should be gradual not introduced at a specific ratio.
Another key understanding is that growing processes reflect the bias of the developer for particular styles and outcomes. Expect to find a wide variety of formulae and or techniques.
You might receive more specific suggestions if you posted a picture of a tree you wish to work with and gave a general idea of the style you have in mind. This would assist all concerned as the techniques and approaches vary with species and stage of development the tree is at.