Best way to transfer a 55 gallon fish tank?

I am buying a 55 gallon fish tank (stand, tank, fish, water, EVERYTHING!)....so far we figure we keep at least keep 70% of the water (in coolers for transfer) and replace the extra 30%. We also, plan to not clean the filter at all, so it can help make the PH level in the water back to normal. We don't want to kill the fish, so we figured we could put the fish that I'm getting (from the fish tank) into my 12 gallon fish tank, till we get the new fish tank set up, and water temp to about 76/78 degrees. I am not a fish expert....and know a little about fish, but nothing as drastic as transporting a 55 gallon fish tank 5 miles away, and brining it home without killing the fish. Please let me know, if you have anything to add to our plan....or anything that should be changed. Any help would be much appreciated. Thank you!!!