I am sure others will have suggestions but let me take a stab at it:
How does prolepsis help defend against skepticism and allow us to be confident in our knowledge?
It provides a framework which points to both a starting point for knowledge and way of expressing how we get to the point of concluding that some things are right and some things are wrong. Epicurus is constantly looking back to the ultimate questions of the universe, such as whether the universe is eternal in time or infinite in size or has any supernatural elements. If you can't point to a mechanism through which conceptual thinking began to be accumulated by living beings, then you are left with the concern that all this - including our thought processes - have been supernaturally created. I would say that prolepsis does for human thought what atomism does for pure physics - it provides a non-supernatural framework of analysis, and then it's up to us to go from there to understand more about atoms and more about the brain. But if you don't have such a framework, then many people will decide just to go with the flow of the gods and never challenge the orthodoxy. When you have conceptual framework for the development of concepts and truth that makes sense, you can confidently dismiss radical skepticism and have confidence in those things that you can hold to be true, vs those that are false and those where you have to "wait" and accept alternative possibilities until you have more information.
Additionally, why is prolepsis necessary for us to know certain things? Isn’t it possible that we simply learn them from experience? I get that Epicurus had to respond to Meno’s paradox, but why didn’t he simply disagree with the whole premise that we need to have some foreknowledge of something in order to know it?
Because there is a root of truth to the question being asked in Meno. How do you conclude that you are "Right" about something if you don't already know what "right" is? How much experience is enough in order to be confident about something? Ultinately there has to be a framework in which you take a position on how much experience, and what kind of experience, is enough.
Something like prolepsis is an important concept within the overarching philosophy even if it doesn’t directly relate to happiness or maximising pleasure.
Well of course I would say that it is absolutely essential to both happiness and maximizing pleasure unless you are confident that pleasure and happiness should be your goal, and that you are pursuing them correctly, then you will be plagued with doubt and all the problems that doubt creates