Custom Fields in Feeds?

I have been attempting this for a while now but not making any headway. I’ve read many tutorials and forum posts, but it’s overwhelming me. I need a good simple place for a layperson to start.

I use several custom fields on my site that I want to incorporate into my feeds. The custom fields in question are: draft (‘old’, ‘last’), version (integer), subtitle (text), intro (html), epigraph (html), outro (html).

I want to customize my feeds to output:
if draft === ‘old’ exclude from feed, else
the_title: subtitle, ver. version
intro
epigraph
the_content
outro

I’m not completely inexperienced— I’m capable of manipulating the output for a child-theme I created: I apply custom post css for draft value through a post_filter. I inject a meta robots noindex in singlepage posts of old drafts, I change the webpage title of single posts to Title (draft, ver), I exclude old drafts from the front page and from Poems category, and I include the other fields in content.php.

But I’m throughly lost and confused when it comes to editing the feeds. The learning curve here is steep! and the logic too great. And there are so many feed related files in wp_includes, and much of the info I’ve found are at least a couple years old and it seems to be outdated—but I can’t really tell due to my lack of experience.

OH, I don’t know if it’ll matter, but I am using Feedburner for post, comment, and podcast feeds.

Does anyone have a good first step for me?