Highlighted weapons are free options.
Sucrose's Ascension 4 Talent boosts the entire team's Elemental Mastery by 20% of Sucrose's total Elemental Mastery, which is why you want to stack as much Elemental Mastery as possible in her artifacts. As a support, most of Sucrose's value lies on her Ascension 1 and 4 talents, hence leveling her other talents (Normal Attack, Skill, Burst) is not required.
When utilized as a (4) artifact set holder, make sure you don't immediately swap away after casting Skill/Burst, you need to be on-field when the Swirl reaction happens for you to trigger the 4-set effect.
There are some team compositions in which Sucrose's Elemental Mastery is not a priority, such as Freeze teams or an Anemo battery for Xiao. In such situations it's better for Sucrose to use [R5] .
Sucrose's talent levels are not a necessity.