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Sia 's laid out the witnesses she plans to call at her upcoming spousal support and custody hearing ... and she's listed herself as chief among them.

According to a new filing, Sia says she expects to take the stand at a hearing for approximately 2 hours on issues such as spousal support, custody, visitation, attorney's fees, and more. Shutterstock Premier

Sia also lists her estranged husband, Daniel Bernad , who she expects her lawyers to cross-examine on various issues like custody ... and accountant Tracy Katz , who she says will testify about child support and other financial issues.

As you know ... Sia -- who is being repped by disso queen Laura Wasser -- and Daniel are going through a very messy divorce and custody battle over their s

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