If I'm going to be the one to start this thing,……
指某个人（这里指自己）来开始这件事
we have been for the last ten minutes.
have been 就是一个完成时,而for对应完成动作所持续的时间长度.
这句话应该是对话情景,接另一方的提问而做出的回答.比如,How long have you been stuck in the tunnel?回答：we have been for about 10 minutes.完整的回答应该是we have been stuck in the tunnel for about 10 minutes.显然中间的stuck in the tunnel被省略了.
those who can walk,head for the main gate.
those who can't,wait,We'll come back for you.
head for向什么方向移动.翻译：那些能走的,走向大门；那些不能行走的,等着,我们会回来帮你们.