Using shared libraries for external scripts, looking for advice (windows)

[Tofu Ninja via Digitalmars-d-learn]

So this is kind of an open ended question, just looking for 
advice on doing it in general, if it's possible, and doing it 
specifically in D on windows. I am not super familiar with how 
shared libraries work so I had some questions.

I would like to attempt to use D to write scripts for a game 
engine I am working on. The goal is to have the ability to 
externalize the code that is specific to an individual game or 
level instead of just compiling it all into the engine it self. I 
want to be able to treat them as resources similar to other asset 
files such as images or models. A secondary goal is to be able to 
reload them at runtime for iteration.

So with that in mind, my general plan was to compile them into 
dll's and load them at runtime. My understanding is that to make 
it work, each dll will need to have an entry point that registers 
its data with the rest of the engine but I am unclear of some of 
the details or even if it is possible.

I am unsure of how to give the library access to the rest of the 
engine. For instance, I have some global data in the engine. How 
do I go about making sure the dlls have access to that data, is 
there a way to make sure the dll will share the memory space as 
the rest of the program, or will I need to explicitly pass that 
data into the dll to give it access.

Also I am unsure of how to go about keeping the engine code out 
of the dll. I would like to keep the dll as small as possible. If 
the dll accesses anything from the engine, how do I keep the 
engine code out of the dll? Idealy I would also like to keep 
phobos out of the dll as well. If the dlls get too big then it 
will probably not be useable.

Is this even possible currently? Is this a terrible idea or am I 
severely misunderstanding things? I think I heard that remedy 
games did something similar, anyone know the specifics of how 
they did it?