The page linked hints the power draw for the Sandisk to be below 3.5W, so it's not that much. If the disk draws 900mA during peak consumption, there's not much left to 1,200mA for the other 3 devices.
You can test by connecting all devices at once and performing some write intensive tasks on the SSD to see if anything disconnects. If that doesn't work, then get a powered USB3 hub.
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