Don't worry about perspective drawing. This is a much more technical subject, separate from the skill of "drawing what you see".

I want to be able to draw from imagination. Drawing from real life has no appeal to me (though drawing realistically does).

Any artist that draws from imagination will tell you to draw from real life. Once you get that down it's waaaay easier since you have strong foundations in figures, perspective and forms. No one just started drawing from imagination.