Szat's Will

There's no extra bonus if you control more than one commander.

Once you've announced that you're casting a spell, players can't take any actions until you've finished doing so. Notably, opponents can't try to remove your commander to change how many modes you may choose.

The commander you control doesn't have to be your commander.

Even though the card is named after a specific character, controlling any commander will satisfy its condition.

If both modes are chosen, and an opponent sacrifices a creature token to the first mode, that token will be in the graveyard as the instructions in the second mode are followed. As it's not a creature card, it won't be exiled, and it won't be considered for determining the value of X. The token will cease to exist after Szat's Will resolves.

If both modes are chosen, they happen in the stated order. Any creature cards that end up in an opponent's graveyard because they were sacrificed for the first mode will be exiled as the instructions for the second mode are followed.