If I'm not mistaken, you were rear ended. There is no argument. Plus you have their admission of guilt if they try to spin things around. You have 1 year to report it and liability should be determined fairly quickly
You take it where you want it fixed Not where they can get it cheaper. Nobody tells you where to get it fixed period. Don't waste your time getting other quotes to try and save them money. if they aren't comfortable paying the 1200 don't waste anymore of your time. Just call their insurance.
Get a quote and present it to him. If he doesn't pay call his insurance and file the claim ( you have 1 year). You won't need to get your insurance involved since he is the responsible party. When u get the quote ask the shop if there may be hidden damages. If there are possible hidden damages let the other party know so he is not surprised when more comes up.
The two guys at fishermans wharf (guy hiding behind bushes and guy holding sign that says "why lie, I want a beer" makes over 100/day and this was several years ago.