Hi Dave, hopefully I can continue to help you out.
Pages and plugins are actually the same thing? Meaning, the default plugins / pages are quite limited in what each is designed for, or perhaps I should say highly dedicated?
Yes Pages and Plugins are the same and can be limited. Most people (if not all) will tell new users to purchase the Stacks plugin right after RapidWeaver
So if I want a page that has a mixture of features found in several plugins I would need to use a Stacks page to accomplish this. Thus allowing me to then work inside of the Stacks page mixing matching varied stacks in such a way to achieve my desired UI for that given page?
Yes, if you want a mixture, Stacks is the way to go. Be sure to check out the new great feature in Stacks 3, Partials. - http://yourhead.com/partials
I am generally familiar with the Foundation framework outside of RW. So what Joe has done is to bundle this amazing framework up into an elegant theam which allows for its stacks to be used inside a RW “Stacks” page (plugin)?
He has worked very closely (been in to their headquarters multiple times) and they have acknowledged him publicly (on twitter) about his success with Foundation for RapidWeaver. Actually more developers (theme) have used Foundation in the past, Joe was the first though to use the ENTIRE framework and allow users to use the Stacks plugin to design their own look and feel to their sites. It currently uses Foundation 5, but he has plans to release a version that will use the current Foundation 6 later in 2016.
If I am getting this so for, what is the main advantage to using the Foundation Theme stacks over the varied stacks that come with the Stacks Plugin and would the “Blocks” by YourHead be similar in concept to Foundation just much more limited in features and functionality?
The stacks that come with the Foundation for RapidWeaver theme are highly tied together. They will make your site faster than using the standard stacks. Now, you can use MOST other stacks with Foundation, BUT unless you are going to code the site yourself in RapidWeaver, you will at least need the Starter Pack to use stacks (this gives you the theme styles and nav system you need in RapidWeaver).
I am also looking at RapidCart Pro 4 which is also a plugin. Since it appears a RW page only uses a single plugin at a time how is this accomplished?
I am not too up to date on using RapidCart Pro with Foundation, but I do know they offer stacks that can work in stacks pages and other users have also used a plugin called PlusKit (by Loghound) to import a Nav bar into a RCP page.
Wether you go with Foundation or not, Joe has a great Google+ Community that a lot of users here have joined as well, you can always ask questions there, but if you do use Foundation, the users there are REALLY knowledgable about Foundation and what works great with it and what does not. If you do decide to go Foundation, I also suggest you look at Big White Duck, he has made some free add-ons for all RapidWeaver but most of them only work in Foundation (although he does have a number that will work in any theme).
Hope this helps and keep asking if you have questions!