Jiraiya could use SM on his own. Pa state Jiraiya could create sage chakra on his own. Here is Jiraiya in SM without the toads -
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- The reason he use the toads was to counter the risk to using SM. If Jiraiya needed the toads to gather natural energy and create sage chakra he would have summoned them prior to activating SM.
Pa frog was even going to have Naruto learn the fusion jutsu so he could use the toads help in battle. It's normal for a toad SM user to use toads in battle because of the risk -
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to
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Pa Frog didn't teach Naruto the fusion jutsu until after Naruto learned SM. He trained Jiraiya the same.
A few second is a long time for a ninja (Minato) who moves at the speed of light.
Itachi, who is known for having less than average chakra, could create Susanoo. Uchiha have powerful chakra. The stronger the chakra the less chakra is required for jutsu.