Dad’s old DeVille needs some TLC, any recommendations before I give up on it?

My father has had this DeVille for years and it means a lot to him, but it has been sitting mostly unused for the past year and now it needs a proper going through. The battery is dead, there is a belt squealing on cold start and I am pretty sure the fluids have not been touched in ages. He does not want to sell it and I do not want to let it rot in the parking lot, so I am trying to find someone who will treat it properly instead of brushing it off because it is an older Cadillac. I came across a mention of premium Cadillac care center at Car AC Repair Sharjah while searching around but I have not made any calls yet. Anyone here dealt with an older Cadillac that has been sitting for a while? What should I expect in terms of what needs doing first and is it even worth putting money into? I am not expecting it to be cheap, I just want it done right.