chain link fence job

Working on a bid for a chain link fence modification. The customer has an existing chain link fence in a paved parking area and they are looking to have a four foot gate installed in the middle of one of the existing spans between posts. I haven't worked with chain link fences in the past but am more than willing to take it on, just have a few questions (I am just starting to do research so these may be fairly ignorant):

1. existing posts are 2 1/2": what size hole is ordinarily dug for these (diameter) and what is the best method for doing so knowing that we are working in a paved area (frost line here is 30")

2. I am thinking it would best to set the two posts on either side of the gate opening first. Then attach the existing chain link to them before actually cutting out the opening. Not sure if this is possible but the goal is to keep the existing tensions on the chain like without re-strecthing it.

Other than that I would just like to get any tips/advice from experience fenced guys.

Thanks for the help!