Pyracantha are good, nice purchase.
If the goal is a 6 to 8 inch shohin size tree, it is important to remove, or cut back any long straight segments. The longest you want a branch to run without a bend, turn, angle or movement change is about 1 inch to 2 inches max. The further out on a branch, the shorter the straight segments should be.
When to do a chop? I would wait until late spring, let the first flush of growth lengthen and begin harden off, meaning the first 4 -6 leaves on new growth are fully expanded, hardened off, and making energy. Pruning at this time will hit the tree at a point with relatively low energy reserves, which on a healthy tree will result in shorter internodes for the new growth that sprouts. Prune back every single branch, leave no growing terminal unpruned. This will maximize back budding. This treatment should not be done every year, or on weak trees, but on a healthy pyracantha will not be a problem.
Wire in autumn or over the winter if needed. Older wood is very hard and brittle, only first and second year wood bends easily. It is possible to bend older wood, but very likely to break rather than bend, so use caution if you are trying to bend older wood.