I have some good news, and some interesting things learned as well.
Taking my sample program as an example, I learned that to include external functions, I needed to both append END after the main portion of my code, before the functions, and also have a function defined in the main file. If I did not include a function in my main file, I got syntax errors.
Also, I was able to make my other code work, but in doing so I noticed that I was getting the duplicate function error. I assumed this was caused by having #include statements (instead of letting the editor handle it), but to my surprise, they were all commented out anyway. So, I decided to just remove those lines for good measure, and finally my program was running!!! Very strange, but I thought I'd share

Btw, the lines I removed were using the // comment, so I'm not sure if this behavior applies to REM.
RAWWWR