Which aggregate appears before...perception or feeling?
The same terms are often used at a "microscopic-view" level, at a "day-to-day-view" level and at a "macro-view". This leads to a lot of confusion.

According to the Abhidhamma, feeling / sensation / experience (vedanā) and perception / recognition (saññā) arise simultaneously in every Thought Moment (cittakhaṇa). The Abhidhamma looks at things at a "microscopic-view" level.

The Suttas (MN 18 is an example) describe how sensing leads to thinking. At this "day-to-day-view" level, vedanā (part of the sensing process that is the same for everybody) leads to saññā (start of the thinking process; a subjective process influenced by latent defilements leading to distortion of perception).

The aggregates are a way of describing what constitutes a being (what a being is or what a being does). This is the "macro-view" level that describes the nature of existence. The aggregates do not have a sequence (they are not describing a process), so vedanākkhanda (feeling aggregate) and saññākkhanda (perception aggregate) arise simultaneously.