Hi G,
Welcome to the wonderful world of precode horror comics! Oh I envy you. You've got so much good (and bad) horror material to read.
EC is your gold standard but unfortunately it's not in the public domain so we can't share it here. But there's many reprint volumes out there to find. Check your local library, many carry the EC archives.
For learning more on the era one of our scanners
Tilliban is very devoted to the genre. He's got a handful of site to check out starting here:
http://fifties-horror.de/ It's in German so you'll have to run that URL through Google Translate or some other such site. Tilliban also has subsites at the bottom that cover Ace; Avon, DC & Quality; Fawcett & Charlton; Fiction House & Standard and a last one on the crime genre.
We have an old topic on here that covers a lot of different books that would help you:
Books on the History of Comic Books you have read or own in your collection! CLICK HEREThe best current Magazines being published on comics is Roy Thomas'
ALTER-EGO published by Two-Morrows. Every issue is great! They also publish
BACK ISSUE which focuses more on the Silverage comic era.
A book that gets talked a lot about in there that you really should give a read is David Hajdu's
The Ten-Cent Plague followed by
'Men of Tomorrow: Geeks, gangsters and the birth of the comic book' by Gerard Jones. Both are wonderful reads.
The
Steranko History of Comics Volumes I and II is wonderful but also very hard to find and can be pretty expensive too. I paid more than I wanted for a couple of reader copies on eBay.
There's a series of comics that was reprinted last year I think called
'Comic Book History of Comics' by Fred Van Lente that is well done. A tpb of it can be found on Amazon.
Two recent reads I quite enjoyed but are specific to artist or character:
Dinomania - The Lost Art of Winsor McCay (2015) by Winsor McCay and Ulrich Merkl
The Secret History of Wonder Woman, by Jill Lepore (Knopf 2014) and a big source material for the 'Professor Marston and the Wonder Women' movie that came out last Nov.
Some books I have in my 'to read' pile though not horror specific include:
Fiction House: From Pulps To Panels... (Yoe Books 2017) by Mitch Maglio
Black Light - The World of L.B. Cole (Fantagraphics 2015)
Four Color Fear - Forgotten Horror Comics of the 1950s (2010) by Greg Sadowski
From Shadow To Light: The Life & Art Of Mort Meskin by Steven Brower (2010)
Out of the Shadows by Mort Meskin, Steven Brower (2012)
Spacehawk by Basil Wolverton (Fantagraphics2012)(Digital)
Take That, Adolf!: The Fighting Comic Books Of The Second World War by Mark Fertig
The Art of Will Eisner (Kitchen Sink Press 1989)
The Blighted Eye: Original Comic Art from the Glenn Bray Collection (2014)
The Secret History of Marvel Comics by Bell/Yassallo (2013)I'm sure some others here might suggest more reading material.
Let us know how it goes,
-Yoc