If you want to invest time, you may want to skip Photoshop. This is a dying product, if Adobe continues its misguided policy. Check the web for the uproar, before investing your time to learn a package than many end users are fleeing from today .
Or...you might not want to listen to Chicken Little
and get to learning Photoshop which is what the OP said he wanted.
I know of no books dealing with taking digital images and making them into old master type artwork...Photoshop CS6 (and CC) has a function that can be used pretty well once you mater it called Oil Paint that can produce some realistic brush strokes (with fiddling).
I think it would be useful to post of original images and some example images that you want to emulate and see what people suggest.