You might also look at some illustrator courses, they rely quite a lot on classical drawing and painting skills. James Gurney, his blog Gurney's Journey and his videos are excellent for doing both landscapes and man-made landscapes and people, he handles all subjects with good realism including imaginative ones. The kind of classical art you're talking about also included mythological subjects and that's where Gurney's books and videos could help.
Also, on that order, there are three books by Jack Hamm:
Drawing the Head and Figure
- human proportions, human portraiture and figurative drawing, all ages and genders.
How to Draw Animals
Just as described, with quite a lot on drawing in general. Covers all sorts of animals and really good on horses, dogs, cats, big animals and small ones. Also textures.
And this one is heavy. Seriously excellent.
Drawing Scenery: Landscapes & Seascapes
- This one not only goes into landscape elements like trees, rocks, buildings, water and so forth, but also composition and planning a painting. It was the toughest of the three to study and may be the most valuable because of it.
All three of them are extremely concise and dense. It takes days to work through a page - and I seriously advise working through the books slowly. Not necessarily in order, choosing a subject you're immediately interested in like Black Hair or Baby Proportions can get you going in an emotionally satisfying way, as long as you skim the whole thing to get an idea of the whole. The third one it's good to read slowly and do all the exercises in the planning and composition stages.
Hamm also has one on cartooning that may or may not be relevant, has some interesting points about motion and action in it. Cartooning the Head and Figure
isn't expensive either.
I bought the set of four, over and over again. I first got Drawing the Head and Figure
as a teenager at fifteen. I think I'm on my fifth copy. I keep wearing them out. When the cover starts to get ratty, I pass it on to someone I'm teaching and replace it before the book's completely dead. That is how valuable the lessons in it are - and how good the index is on every one of them, because if I need information on a specific subject it's always easy to find in them.
You can also download books by Andrew Loomis online at various links, google his name. They are similar to the Jack Hamm book, especially Head & Figure, with many of the same exercises. Lots of good information in them and those downloads are free - but the physical Hamm books have their own benefits being offline and possible to copy from them.
There are a good many oil painters doing videos on how to do classical oil painting, with all its extensive layering and chemistry.
I think that with diverse sources it's easier to develop your own style, pick and choose the techniques you want. With an atelier there will be a school style, there will be fairly rigid but definitely effective ways to do everything you set out to do. However, not much in the way of comparing the different ways. In general in oils you'll do a sketch in thinned sienna with turpentine, a value sketch, very loose, to plan the painting. Then over that a detailed grisaille, a black and white realistic rendering done very carefully. Usually using a black tube and a white tube. Then over that painting various glazes and layers with increasingly more oil in them, letting them cure before you go adding more layers. Then wait for that last oily layer to dry and cure, then varnish it a year after you painted it. Then it will last for centuries and have the luminosity of Old Masters.
The Hamm books don't teach anything about color, sadly. They cover everything but color. There is a class here on WetCanvas that influenced me tremendously on color handling, it's "Still Life the Colourful Way" by Colorix, to be found in the Soft Pastel Learning Center forum. I was one of the original students and that completely changed my view of color, the way I see color, the way I mix colors and handle them. It's not classical though, it rests more on the Henry Hensche school of Colorists. The knowledge can be applied to realism though, especially when it comes to mixing color.
In addition to that class, James Gurney in both of his print books, Imaginative Realism
and Color and Light: A Guide for the Realist Painter
- heh, yeah, Gurney does realism. How well, you'd have to get a look at his videos. I'm in awe of him.
His method of painting imaginary creatures is to sculpt small maquettes of them, paint those true to color as planned, then set them up in lighting conditions similar to those in the painting and proceed. This may include backdrops for the maquettes. He does very realistic paleo art including illustrations for Scientific American,
along with his own dinosaur fantasy series, Dinotopia.
I've had a lifelong love of paleo art and my view of classical painting always involved Charles R. Knight as much as any artist featured in an art museum - and of course all the brilliant backdrop painters who contributed to the Field Museum's dioramas and displays. So naturally I was drawn to Gurney's work. It's a subcategory of realism, but he handles other realist subjects as well as his prehistoric birds and reptiles.
Anyway, hope these help. I do think it's possible to get just as good without going to a formal atelier. I also think it's possible to get that good with a good illustration course, rather than a fine art course, then turn it toward fine art by choice of subject and market.
The best way to get that good is by doing it a lot. Sketching and drawing constantly will improve your skills, especially life sketching anything. Start with inanimate objects including sleeping animals and people. I started my animal studies with my cat. For over a decade I sketched him constantly, by the time I was really familiar with cat anatomy I discovered I had a much better grasp of other animals' anatomy as well.
Oh yeah, don't discount those assorted anatomy books, human and animal. The classical painters attended dissections or did them. Understanding how muscles and tendons interact with the skeleton and how bodies move in space, how they bend is really important to figurative painting. Manikins often have a greater range of motion than real people. Dolls and action figures may wind up with both less and more depending on type. But those can also work as maquettes once you understand what you're looking at. They won't show the muscle moving over skeleton in various poses.
For that, self portraiture is the model who's never tired of posing. Look in a full length mirror and take different poses. Look at what gestures do to the shape of your arm or your leg, sketch it. Fill sketchbooks with things like that. Constant observation of reality will take you where all of them go, because we are all put together like human beings.
So have fun with it.
The one thing courses are good for though, is to fill in gaps. Feedback in places like WetCanvas helps too - again to identify gaps, things you didn't think to study when self taught. I had a few weird blind spots and while I'm loosening up now on a lot of things, I still don't entirely want to loosen up. More learn to be capable of being loose in areas that need to be looser because they're not the central subject.