I grow mine in full sun to part shade in a very fast draining mix. The mix you mentioned sounds much too moisture retentive. I have some that are doing well in pea gravel and calcined clay. I have some in the ground that only get natural rainfall which amounts to about 15 inches a year with 100F+ summer temps and they handle it like champs. You can prune them into a formal hedge if you want. So yeah they respond to pinching/pruning. The broken piece should root easily. I let my cuttings callus over before planting them to prevent rot.

mine grow in the ground in just about any soil I have , from nearly pure clay, to sand. They all seem to do pretty well... very adaptable plant. I have some in full sun, and some in nearly complete shade... doesn't seem to make much difference.

During the Winter, give them as much light as possible.

I grow mine in fast-draining mixes and I make sure that the mix doesn't get too dry....
or else the leaves start dropping. If, on the other hand, the leaves turn yellow...too much water.

During the Summer, outdoors in full sun, watered and fertilized regularly.
I've also rooted cuttings directly in my garden soil, then dug them up in the Fall
and potted them for friends.

Josh