The things that affect what JY cares about are what he pays attention to. He was concerned about his house, house value, taking a hit on the house. He talked to his mother and mentioned it to LF on the same day his wife is murdered. That tells me his house is on his mind in a major way.
So he did things to preserve his house, at least what he could do after he got his rage vented on his wife's head.
Contain his own mess to the MBR, use garbage bags (garbage bags were out on the kitchen counter), not mess up the downstairs at all, pick up CY and carry her to her bathroom (note he used her bathroom, not the master bath), use a hose outside, etc. Why a random murderer would care about containing a mess at that point makes no sense to me. Only the homeowner would care. Random perp who is not supposed to be there wants a quick exit. Something gets damaged or messed in his wake, is not his problem.
To me it's obvious his goal was:
1. Get in quietly, kill Michelle easily with a soft kill of strangulation, get out
2. Once the kill turned messy it was, get clothes, contain bloody clothes, don't track mess in house, don't track any evidence into car.
3. Once he realized CY was not only awake but in the room he added: contain CY mess, put CY in her bathroom, clean up CY enough to contain further mess, get CY back to bed and asleep.
4. Above all, don't get caught, don't talk, discard anything that can be discarded to tie to the murder, the scene, etc.
5. Get MF to house on pretense of picking up a computer page printout so she can get to CY and be the one to find body.
