Blueberry makes a great Port-style wine, but Peach is such a light flavor that it'll probably get lost in the mix.
For a 1 gallon batch, I'd go with 6-8lbs of blueberries; keep it warm, because blueberries naturally contain benzoate, which hinders fermentation.
Depending on which method you want to use, kind of dictates the approach. You could start with a slightly-higher SG (in the 1.100-1.110 range), with plans to stop it somewhere between 1.010 & 1.030, depending on your intended final sweetness, using about a whole bottle of brandy to alcohol-poison the yeast into killing the fermentation
I havent done the math, just need to run your intended ABV through a Pearson's square with some 40% ABV Brandy, or higher-proof liquor if thats how you roll; i dont, personally, i use Brandy - but this will let you know how much Brandy/liquor you'll really need to boost the ABV high enough to knockout the yeast
Or you can ferment to dry, add brandy and possibly sorbate if you favor taste over abv-high-enough-to-kill-yeast, and then back-sweeten the wine from there.
Nothing wrong with either style - it's all about what you like, and how you want to achieve it - although the first option is more 'authentic' than the second... They'll both work.
You'll want to make sure you have your nutrient additions, and maybe add some additional things like Opti-Red or Booster Rouge to help boost color stability, enhance the mouthfeel.. Maybe even tannins.. You're looking at making something thats a little more flavorful, a little higher in alcohol, and its gonna take some sweetness, some mouthfeel, and the right acidity to balance that out into something you look forward to drinking