Sounds like you're starting from the ground up. In that case keep it simple for now, just use a trusty No.2 pencil and some printer paper or newsprint. No need to fight with mediums while you're already fighting with the basics, just keep with the pencil 'n' paper and practice practice practice.
Loomis is good, but I'd suggest checking out Nicolaides' "
The Natural Way to Draw" as well. There's an old saying that goes: "It takes 1000 bad drawings to get 1 done right", and Nicolaides definitely has 1000 drawings worth of exercises to burn through.
So keep plugging away, don't stress if you don't like how your drawings are turning out, just focus on getting better each time.
Once you've filled out a few sketchbooks worth of drawings (if you're doing Nicolaides' exercises or something similar that won't take too long) then you can start trying out some different mediums just to keep things interesting and fun. Also now that your drawing arm is all nice and limber from cranking out 1000 bad drawings, it'd be a good time to start working on particular subjects like anatomy or perspective.
And yeah, traditional mediums will transfer over very well to digital work. Lots of digital painting tools are based off of traditional tools, so it's not much of a leap if you already know to work traditionally.
Oh and don't forget to occasionally ignore the above advice and try to do something way over your head. Gotta keep it interesting to keep from burning out. Gets too boring if you always do what you're supposed to.

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