From my knowledge, diluting the minoxidil as you are doing is not something I would say is a good idea. I can completely understand that normal, full-strength minoxidil might have caused your scalp burning. There are a few components to minoxidil that often cause that kind of reaction in people.
However, numerous studies have shown that diluting minoxidil reduces it's effect on hair regrowth, over time... and the reduction is exponential in nature. Using .5% minoxidil as you are, as opposed to the 5% that has been shown to maximize hair regrowth potential means your chances of seeing sustained regrowth are slim.
I don't mean to be the bearer of bad news here, but this MB is also supposed to be about honesty, and honestly speaking the pigmented vellous hairs you see are not at all a guranteed sign that those same hairs will inevitably become terminal. It's a common 'first thing' that minoxidil users see, and they often delude people into thinking that they will be looking like David Schwimmer by spring when in fact only a small fraction of those hairs will end up long on the first cycle of regrowth.
Additionally, I think the dilution of your minoxidil is indeed helping your scalp because you are reducing the amount of PPG, a common irritation-causing ingredient in minoxidil, that you are applying on your head. In effect, the PPG probably caused your burning reaction (and, btw, scalp 'burning' is a classic symptom of PPG irritation), and once you started putting on the diluted minoxidil, with only 10% of the original level of PPG, the burning stopped.
As for your nutrient solution, I don't think it would have any effect whatsoever on your scalp condition unless you are also mixing in some sort of skin-penetrating vehicle chemical into your solution as well. Your skin is waterproof, so any nutrients you try to dissolve into water and apply on your head are most likely drying and sitting right there on your scalp, which is dead skin. The only way a nutrient could actually do any good to a follicle would be if it were dissolved in some sort of alcohol, PPG, DMSO, or other known penetration vehicle. Then, it could actually get THROUGH the skin and to the hair follicle and potentially do some good.
That being said, what nutrients are you putting in your solution? Most nutrients have to be absorbed in the gastronomic tract, where enzymes can break them down into usable substances. For example, grinding up a vitamin and putting it into a skin-penetrating vehicle such as alcohol, and applying it on your skin will not get you any benefit. Sure, the vitamin will enter the skin, might get into the lympatic tract a bit and from there into the blood, but because the vitamin has not been 'digested' as orally eaten vitamins are, it is more than likely being pissed out.
I know I am sounding negative and I don't mean to be. I am honestly trying to help you, give you some good advice so you can get the regrowth you want and minimize the burning side effects. To do this, I think you want to KEEP using minoxidil at 5%, but try a variant of it that is free of the most common irritation-causing ingredient in minoxidil, which is PPG. You can buy 5%, PPG-free minoxidil from Dr Lee, who is a very reputable hairloss products sales website. I think is both worth a try, and in your best interest. I would hate for you to be spending all that time dripping a liquid on your head every day, day in and day out, only for you to figure out later that you have shot yourself in the foot by not using the FDA-recommended level of minoxidil that is statistically shown to give the good stuff, the regrowth.
All the best, and good luck with the fight.
Gard