In my opinion, drawabox is great for developing eye-hand coordination: I really wish I had known about this in animation school, where I realised my motor skills sucked big time, while my teachers kept repeating that I should draw more. However, after the first fistful of exercises, drawabox is less useful. The value of Drawabox is not in drawing boxes.
As a beginner, use any medium you're comfortable with. So, if you feel Krita gets in the way, leave it for now. In general, there is nothing fundamentally wrong with digital, just don't overly rely on undo. Try to get it right first time.
I went to art school at age 42. In my experience, you will learn slower, in particular when it comes to motor skills, like eye-hand coordination and line quality; also, you may have less energy than the kids around you. However, you will probably learn more efficiently, due to experience with planning and self knowledge, and you are likely to be better motivated than your younger peers. You may run into preconceptions from employers not hiring you: age discrimination does exist, unfortunately...
Bought some Fabriano Accademia, only to find I don't like its rough texture. Yes, I know charcoal needs 'tooth', but the texture here makes it impossible to shade a smooth midtone. I noticed Proko uses Strathmore, but this is hard to find here in The Netherlands. Could someone out there recommend a smoother charcoal paper? How about Fabriano Tiziano?
In my experience, the overhand grip allows you to separate the location of your medium, using shoulder and elbow, from its orientation/character, using wrist and fingers. The latter is particularly relevant when using a softer medium, like charcoal or Conté, on an easel. In addition, I see it as a teaching tool, forcing students to separate the two mechanics. Once you get it, anything goes. I know people drawing really well from the dreaded monkey paw, which I do not recommend at all for beginners. And, of course, using a stylus on a tablet changes everything.
Hey Chrystal, Good job working on the Loomis head. The thing I notice the most is that your lines do not wrap around the shape of the head. The skull is a 3D shape, so make sure you wrap the lines around it. I did a quick sketch to show you what I mean :)