Yes, just go to local service center to do it. search in this forum. you should find a lot of posts for FP.
(2)deadline快到了,我們現在給USCIS寫信來得及嗎?
it's always not bad to write to USCIS.
(3) 這是我們的第一個手印,是不是說我們的case已經開始處理了?
might not. maybe they begin to document it.
(4) 如果是的話,是不是3個月左右我們就可以拿到 EAD和AP了?
good possibility but not guaranteed.
(5)現在是不是就隻有等待結果?
yes. What else do you want to do?