The fundamental problem is oil. The huge abundance of oil in Venezuela is both its blessing and its curse. If a country has one overwhelming source of wealth, then naturally it focuses on that to the exclusion of everything else. The endemic poverty in Venezuela is I believe a direct consequence of its oil wealth. Its over-reliance on oil is an example of the economic phenomenon known as the 'Dutch Disease'....
...But beneath everything, oil is the cause.
Here I disagree with you. It is not the oil, it was the Chavista policy of practically basing the economy only on oil when the price was high in order to carry out populist policies by showering the people with money. The saying: feast today, famine tomorrow applies better than ever here. You talk about Dutch disease but Norway as I mentioned before managed its oil and gas discoveries very well.
I do believe that in general Chavez was well-intentioned, but he didn't manage Venezuela in a sustainable way.
I don't know if he had good intentions or not. Like many communist leaders, I don't know how they could have gone from trying to protect the poor, for at least that was the initial discourse, to mass murder of the poor, either directly by mass murder like Stalin, Pol Pot and others or indirectly by starvation.
Caring about the poor implies empathy but killing them is for psychopaths, so I do not know if they were already psychopaths and the initial discourse was an excuse to gain power, or they were someone who really cared about the poor and once they gained power they lost touch with reality and to stay in power and their political project became more important than the lives of the people.