A complicated interaction with Sakashima's Student
After Step 5, you would have to sacrifice Sakashima's Student or Etrata, The Silencer.

706.2. When copying an object, the copy acquires the copiable values of the original object’s characteristics and, for an object on the stack, choices made when casting or activating it (mode, targets, the value of X, whether it was kicked, how it will affect multiple targets, and so on). The “copiable values” are the values derived from the text printed on the object (that text being name, mana cost, color indicator, card type, subtype, supertype, rules text, power, toughness, and/or loyalty), as modified by other copy effects, by its face-down status, and by “as . . . enters the battlefield” and “as . . . is turned face up” abilities that set power and toughness (and may also set additional characteristics). Other effects (including type-changing and text-changing effects), status, and counters are not copied.
704.5j If a player controls two or more legendary permanents with the same name, that player chooses one of them, and the rest are put into their owners’ graveyards. This is called the “legend rule.”

(Emphasis mine)

But let's say the legend rule didn't apply.
Your plan would work. The following choices are made when activating an ability:

Choice of mode[CR 601.2b]
Choice of targets[CR 601.2c]
Choice of how to divide/distribute an effect among one or more targets[CR 601.2d]
Choices that affect the cost to activate or how it's paid

All other choices, such as choice of creature to copy as Sakashima's Student is placed on the battlefield, are made on resolution.