回复：孩子都快能打酱油了，请教各位大侠

续I-20 is free (although you need to show financial statement, but you need to do that for marriage based GC too). Unless the purpose for F1 is not to study but to keep legal status so you want to quit school as soon as possible? I don't see the advantage of not to extend I-20.
You can mail out I-131 (with I-485) the same day after your hu*****and's oral ceremony, but you need to wait for the AP approval before you leave US.