If I wanted to check to see if there are specific codes to what type of lines can be run together in conduits, where would you suggest I start?
The National Electric Code is the place to look for information on that. The Electrical & Lighting forum is the place to post the question. There are several people who watch the site who know the National Electric Code very well.
Electrical & Lighting - Ask Me Help Desk
Although they know the code, occasionally they're somewhat arrogant and they don't seem to like "non-professionals" like me to answer questions there. Nevertheless, they do know their stuff.
There's also a post specifically about where to locate the National Electric Code by guy who goes by "KeepItSimpleStupid". (He's not one of the arrogant guys.)
https://www.askmehelpdesk.com/electr...ne-270277.html