From a harm reduction point of view that assumes you are going to use regardless, then yes you are reducing harm by taking in good nutrition and sleeping.....those are crucial in maintaining your health as best you can given the circumstances.
Ultimately what you put in you get out, if I'm recording a vocalist/singer and they don't sound very good to begin with and whilst there are a million tricks I can do to improve pitch and slap on various effects in the end they can only sound so good. Put shit in and you get shit out. I'm certainly experienced in integrating a large IV meth habit into my life for long periods of time, once you can eat and sleep properly you will perform well.....but you're addicted to meth and that will become a serious issue in your life depending on your family, if any, circumstances.
But if you can keep eating and sleeping and everything else you mentioned then you'll keep it together much longer - mentally and physically. Take care and good luck.
