Hi J,
You must be really commited to stick with draw a box for a year, I know I could do it. I think that it shows in your work though, because you have really confident line work and I do get a nice sense of the pose in your gesture drawings.
I think whether to go with fineliner or pencil is a persona choice depending of what you prefer. I think fineliner or any permenant pen/marker is great for gesture drawings because they should be quick and it removes the ability for you to go back and change your drawing meaning that you will build confidence more quickly over time because that is what looks better. However, that can also be a negative when trying to correct glaring mistakes.Using a pencil can allow you to slow down review your drawing and make changes where you see fit. this can help when trying to get a feeling for a figure in proportion 'feels' like. I would say definitely try out a pencil and see where it take you. Getting the proportions correct is tricky and you are doing really well for only drawing figures for month so dont stress to much about it I think you are doing great just keep practicing. Simplifing the body into its basic shapes can help with getting the proportions. You can check on videos by Proko if you havent already.
All the best !
Congrats on getting back into drawing after a little bit of hiatus. It is always difficult getting back into it after a break!
I think that if your goal is to improve proportions and shape language I would say to slow down and focus on the construction of the figure. Practice simple poses and measure out your forms so that things are in the right place. Gaining an eye for proportion takes a lot of practice I think, so getting in as much focused practice to train yourself to notice when the proportions are looking off will get you to where you want to be. Breaking down the figure into basic shapes can be really helpful.
All the best of luck!
