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It has been many years since university for me, so I’m basically new, want to begin a writing a novel that has been in my head for many years.
How many lines between dialog is the acceptable?
Same question for paragraphs, or scene breaks?
Internet research has given me conflicting answers, and I don’t trust them. Insights? Advice?
I would suggest that you start typing and allow yourself to write a bad, messy chaos of words, sentences and scenes.
The entire concept of Scrivener is to separate the writing from the formatting of text. You can start writing any time and Compile a resulting output document when you’re up to it.
People write entire novels before even thinking about line height, space around paragraphs of dialogue and white space.
A scene without any dialog or scenes containing only dialogue are no exceptions. Between scenes, one empty line suffices. A chapter is a folder and a scene is a document in that folder.
Go write. 
The most common convention to demarcate paragraphs — and you can confirm this by looking at a few published novels — is to have paragraphs set with an automated first-line indent and with no space between paragraphs. There is no special line spacing for dialogue. A blank line of space between paragraphs is used to indicate a (shot or) scene break.
That said, since Scrivener let’s you set up your writing environment independently of the finished look you want, I set my default paragraph in Scrivener to automatically yield no first line indent and a full line of space after. For several reasons: i) it is much easier to find your way around amongst your paragraphs when editing, and ii) it is good to be able to see very clearly in writing how your paragraphs are breaking, and finally iii) having automated spacing between paragraphs will curb the impulse to put double carriage returns between all your paragraphs! Eventually, when you want to compile your draft, you can tell Scrivener to put the text into some nice bookish font and have it change the look of paragraphs to what is described in (1).
As others have said, a great virtue of Scrivener is that you can pretty much just set in and focus on just writing and not worry about typesetting matters. The big challenge you are facing is getting that story idea out of your head and into some kind narrative of shape — we are a long way from typographic concerns!
I appreciate the insights. My outline and character sketches are in the can. I know how my story begins and I know where it will end, and the journey to get there. My concern was after 20,000 words I’d discover my format is all wrong and have to do something else.
I’m just a simple kind of guy. I’m new to the software but a quick learner having been around computers since the dawn of Apple when the fire department plunked a unit down on my desk in 1984 and said, “here learn how to work this.”
What I take from the replies just get the project out of my head and on paper and any formatting issues the software can heal later. Is that accurate?
Yes, but … @gr’s advice is best to follow.
How it looks as a draft and how it looks as a published book are going to be two different things. You’re going to have multiple rewrites to worry about before you get to the publishing stage – and how it gets laid out on the page will depend in part on your publisher and their house style.
One of the strengths that Scrivener offers is that you can tweak your compile format after the fact to produce different output without having to completely reformat your manuscript. Worry about the output later.