Marshmallow there are loads of threads on the Christmas section about Dishwasher Vodka ( Iit's a Thing 
)
I used a bottle of vodka (supermarket own brand) split into 2 bottles (DH had an empty whisky botlle - rinsed well)
I used the purple in one bottle , red in the other . Loads of recipes split all the colours up and you make mini Rainbow Bottles as gifts ( I ate the other ones) some put them all in , but the colours aren't as pretty
We didn't need to run it through the DW they dissolves really well . The filtered vodka was clear red/clear purple .
Store in the fridge it goes like syrup.
If you do put your bottle through the DW to melt whatever you put in, 50-70% fill with vodka and add the amount of chocolate/sweets in the recipe . Leave a space for liquid expansion.
I don't know if there's a maximum , you can always add more .
It depends if you want a vodka with flavour or more a liqueur type liquid sweeties !
Wrap the bottle in clingfilm (in case it ruptures you don;t want a load of broken glass) , put your bottle through a hot cycle , let it cool a bit , shake , check it dissolved .
Mars Bar works well ( not that I'ved tried it) so Frys Chocolate Cream should too .
We should all do a trial in early Dec . Pick your favourite then compare .
I'd try Sherbert Lemons for my DS ( he's got a bottle of vodka hanging about .)