I’m a little worried that the 2:1 ganache may be too liquid for your purposes. Often that ratio is used for a whipped ganache because it is too soft for frosting (unless you are using a very high % chocolate). Perhaps consider making up a small amount and letting it set at the temperature that you would like to serve your cupcakes. Or you could check RHC, I believe there is a ganache center recipe as part of Rose’s lava cakes. I suspect that the correct ratio will be something like 1.2 to 1.
Not sure from your description if you are filling the baked, cooled cupcakes with ganache or trying to bake it into the batter, the first option is probably easier. And chocolate pastry cream would be fine if you are filling baked cupcakes.