I want to develop a good intuition of concepts in Physics, and I've heard that the Feynman Lectures on Physics are very good for this. However, I've also heard that the Mathematics is very complicated. I was just wondering, just how much Math do I need to know? I love Physics, and I'm willing to put in the work. How much time do you guys reckon this will take? Thank you :)
This answer from a question cited in @Davidmh answer has a lot of good info. I thought I learned a lot from the Feynmann lectures when I read parts as an undergraduate. It wasn't until I reread them after getting my PhD that I realized how much I had missed on first reading. My opinion now is that they are not good learning tools, but are fantastic tools for giving context and understanding once you have some background.
See for yourself. Take a random chapter (see all of them here) and you will find mostly vector calculus for mechanics. There is a full chapter on vectors, so you should be fine. Other parts use differential equations, but they are introduced softly.
In general: you need some calculus in one variable and some vector algebra. Being confident with the concepts will help you (so you follow what an integral is, and what the integration limits mean), but you don't need to be able to solve complicated expressions (for the theory and most exercises).