Pruning typically serves to stimulate and encourage growth, so whatever method you employ will be an ongoing situation. FWIW, most ceanothus DO have a habit that is spreading and tend to grow wider than tall. But they tolerate pruning and shearing well as long as they experience such treatment consistantly from an early age and not when they become extremely overgrown. My own Victorias (very well established and approaching 20 y.o.) are easily 8 or 9 feet tall and equally as wide and get a pretty good pruning each year but resume their former size quickly. I've now begun to thin and trim them up into more of tree form so they are less of visual barrier along my drive.

This wants to be a pretty BIG shrub - I hope you have it sited accordingly as I think it is a mistake to try and confine to too small a size.

Actually, pruning does not usually stimulate growth. It may seem that way, and in a few situations may be that way. There is a plant hormone in tips of branches and leaders, that moves down and "restricts" shoot growth. Removal of the ends removes the hormone production points, thus removing the restriction. So pruning in many cases allows other growth by removing the chemical control. The "encourage" aspect is probably the more practical way to describe it.

Master Gardeners and Garden Club members have enjoyed this part of lectures quite a bit.

That Ceanothus is very unique. I trained one from a 5 gallon plant into a 7' tall tree in 2 years.

You need to prune from the inside, lightly thinning, and removing a few lower limbs.

What's challenging, is that the smaller twigs are arranged in a pattern uncommon to many shrubs. And the weight of the foliage and limbs may cause sagging.

Rarely do I prune limbs shorter, almost always working from the inside. But on that plant, it was essential to slightly shorten some of the longer limbs. And it takes a bit of thought to find the right lateral twig that will be good for a new branch end and be pointing the right direction.

The plant will look marvelous as a tree, but take a bit more time on it. Think about the cuts more. Maybe study it one day, and come back again the next, if needed.

I have 20 of these shrubs planted 3' apart in order to produce a 7-8' hedge eventually. They were planted 13 months ago along the back of my home[5' away]. How should I prune these plants [individually or as a hedge by shearing the tops and then the sides]? When is the best time to do this, and what should be done to invigorate growth?

No need to invigorate growth. Guess you won't be walking out back with a plant like that 5 feet away. Thining cuts with a chain saw to the base is the easiest way to remove wide low branches. Base cuts are best either early with loppers or later with a chain saw. They don't seem to mind.
Don't waste time shearing!