Where can he be placed on the spectrum of ideologies?
Populism – is part of the story since he was for the people against the elites. But populism is a notoriously slippery category. Almost all leaders in democracies give off a populist pose.
Anti-imperialism or third worldism – Chavez was indeed a vocal opponent of United States imperialism. It strikes me that anti-imperialist third worldism is populism at the international level: similarly for the wretched of the earth against the global elite, similarly with both left- and right-wing variants, similarly demagogic, similarly slippery when it comes to actual policies.
Militarism – a leader who frequently wore military uniform would (if in the West) soon be called a militarist. Chavez regularly wore uniform.
Socialism – Chavez was for redistribution to the poor and political control of the economy.
Caesarism – Chavez was for strong leadership. He was the caudillo. In fact, I am inclined to place this as perhaps the central plank of his ideology.