]] Was he expecting the elder Mr. Dashwood to outlive him by more than a year?

I think everyone was expecting that. We don't have an age for him , but probably he was only in his late 40s or early 50s.

] I felt as disgusted by the elderly Mr. Dashwood's actions as by John's because he, in fact, initiated this business of giving the John Dashwoods the power of exerting their meaness over the lady Dashwoods. (snip)The Dashwoods, "not merely from interest, but from goodness of heart gave him every degree of solid comfort," companionship, attention and affection. John contributed merely the visits of a cute and noisy child. What could the gentleman have been thinking?

IMO, the point here is not that the old gentleman didn't appreciate his nieces and their care for him, but that what he did was a reflection of what society was like at the time. Because they were women, they didn't really matter, or at least not nearly so much as seeing the Norland property secured to the male blood line of the Dashwood family for at least another three generations.

I'm not sure whether Henry Dashwood ever gave his uncle any inkling of his intentions for Norland, but it sounds as though perhaps he planned to either sell off or rent out parts of it in order to get money for the girls:

"it was secured, in such a way, as to leave to himself no power of providing for those who were most dear to him, and who most needed a provision, by any charge on the estate, or by any sale of its valuable woods."

As a point of family pride, especially for a family that had owned a large estate for many generations, it probably was preferable to the old man to make sure the entire estate passed down to a male Dashwood than to see to the comfort or dowry of three girls. With no son of his own, this was the enxt best thing. I guess women just didn't matter that much at that time when stacked up against a family's wealth, property, respectability and social standing.

]He had plenty of time (what, ten years?) to observe that John is a cold-hearted selfish young man greatly influenced by an even more cold-hearted and selfish wife.