I was diagnosed with diabetes several years ago and started making chocolate for myself rather than do without!
Allulose may impart a change in flavor, but then so does the place of origin of the beans. Erythritol is another sweetener that you might use to cut the expense of Allulose, but I personally wouldn't go above a 50% mix. I'm tending to go back toward mostly or all Allulose.
Another consideration is that milk chocolate will have more impact on blood sugar than dark chocolate. The lactose in milk (milk powder) is a factor. For this reason, I like to substitute heavy cream powder in a diminished quantity. With milk products, the higher the fat content the lower the lactose. You really need to go through a lot of calculations to get a decent balance. My goal has been to keep the chocolate within standard definitions of chocolate with the single exception being the alternative sugar. That keeps me within certain constraints that you may feel are too rigid.
As I've experimented, I've found that the artificial sweeteners affect the viscosity of the mix, making the batches thicker than with sugar. They are also less sweet - only about 70% as sweet as sugar. To make it as sweet as regular (commercial) chocolate, you have to add more (or a super sweet additive which can have a foul taste) - and when you do that, you have to add more cocoa butter to thin out the batch. That means you don't have enough beans or nibs to give it the chocolate flavor you wanted in the first place! It is a real balancing act.
What that all means is that my milk chocolate is on the darker side of a milk chocolate.
I can give you a starting point using Allulose as the only sweetener and whole milk powder, then you can experiment from there. But it is likely that you won't be able to get it either sweet enough or "milky" enough without resorting to using other non-tradional ingredients.
THIS IS UNTESTED... but it is based on my earlier efforts:
All ingredients are net weight in ounces.
Nibs = 5
Cocoa Butter = 5
Allulose = 5½
Whole Milk Powder= 2½
Total grams "sugar" (from lactose) would be about 1.5g/oz.
This will still be a "milk chocolate on the dark side!" making one pound of chocolate. You can multiply the amounts to make what suits your melanger, just use the same factor.
Cheers,
Jim B