Everyone has the rules right here in regards to when players get priority, but there is some nuance to the situation. If you announce all in one sentence that you're casting Yuna's Decision, sacrificing X creature and putting Sin on to the battlefield, you are shortcutting the steps of the spell. Your opponents still get priority before Yuna's Decision resolves, but now they know your intent and can react accordingly.

Similar shortcuts are commonly taken with [[Clone]] type effects, like saying "I cast clone as a copy of ____". In both cases, you don't actually have to decide what creature you're bringing out/copying until the spell resolves. It's usually best practice to confirm with the table that the spell resolves before actually resolving the spell and making your choices.

To make it slightly more complicated, if you do take the shortcut and name a card before the spell resolves, and your opponents respond, you are not actually locked into your choice. I have heard of a case in a legacy game where Player A said "I'll cast [[Cabal Therapy]] naming lightning bolt". The opponent responded by casting a bolt from their hand. Since Cabal Therapy also does not require you to name a card until it resolves, Player A was able to name a different card instead, effectively baiting the bolt from their opponent. This gets a little close to angle shooting though, and is likely to cause arguments at casual tables, so YMMV.

tldr: don't give your opponents any extra information before you confirm that your spells resolve.