PS. I thing 5 months is fine - I had very basic Spanish when I arrived in South America, but did a 2 week course soon after arrival. You can do courses in Mexico/anywhere really if you need to and want the basis for your journey. It's great for haggling/getting to know the locals better. The Lonely Planet phrase books are good, as they give you the pronunciation too - that's how I began with the Portuguese for Brazil.
I didn't go to Venezuela, but my friend Kev did and had a great time:
Kev's travelblogIt was a few years ago, but I've posted his link above in case no one responds specifically on Venezuela here - you can also do searches by countries within travelpod