There are lots of resources out there. Where to start? One thing I would say, is learn the history and learn typography. This will be your most powerful tool and poorly used will always expose a bad designer.
The other thing I would say – apologies if you already know this – but although you are obviously going to be a visually literate person, to shift from fine arts to design requires a complete head change. Design has very, very little to do with self-expression. It is visual communication – taking someone else’s thoughts and ideas and communicating them visually.
This is the bit you need to get right. Too many people get into it because the end result is visually appealing and they ignore, or rather neglect to acknowledge, it is less about the designer and more about the client.
That said, self-initiated projects, outside of commercial work are necessary for the creative feed.
In terms of books to read, before you even get into design practice theory, learn about purpose. One book I read at university – and on that has stood me in good stead ever since – is Design for the Real world by Victor Papanek. Written in the 70s, it is arguably, even more pertinent today than it was back then, in terms of how design (graphic, or otherwise) can help have a positive effect on the world. Graphic design is an incredibly powerful tool and can have a considerable effect on peoples’ behaviour and habits. If you can use this for good, rather than simply selling crap to people that they don’t want to need, for me is the fundamental thing to lean about graphic design, before the practicalities of how to do it. It requires some psychology, some behavioural sociology, as well as all the direct practical theories.
After that, learn from the greats and not the mountains of dross the internet is littered with. Study, Guttenburg, Caxton. Learn about moveable type and how it freed up the ready dissemination of information (good and bad). Learn about Milton Glaser, Massimo Vignelli. Saul Bass, Paul Rand, Alan Fletcher. I could go on…
There will, of course, be cross-overs from your area of expertise, Beardsley, Mucha, etc.
In terms of typography (in no particular order); Max Miedinger, John Baskerville, Herb Lubalin, Mathew Carter, Adrian Frutiger, Claude Garamond, Stanley Morison, Jan Tschichold (his Treasury of Alphabets and Lettering is worth a read). Eric Gill (read his An Essay on Typography – but don’t look too closely into his personal life, if you are of a weak disposition!!), Giambattista Bodoni, etc. More modern people to look at in this field, Erik Spiekermann, Neville Brody, Johnathan Barnbrook, Fontsmith (one of my particular favourite foundries) I could go on for ever and still miss out hundreds of amazing, influential designers.
There are a few threads kicking around here that have asked a similar question to you, so if you have a search here, it will bring up a lot of useful information.
Hope this helps a little.
Good luck and stick around.