For T3 united yes you can
Yes, there is a walkway to T3 before and after security
No.
If you leave international security screening area, no. If you leave customs area, no. Since customs is only in that one terminal, you would have to clear customs again. But between security and customs, you can throw a luau. Lol
Doubt it, but call your airline to be sure. Also did you look at an online map of SFO?
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