5/8 drywall will slow a fire down but it’s not a answer by itself. I would install with a space around the safe,preferably filled with rockwool.Sorry about your family member,what a nightmare.
Pre 2003 treated lumber is tough to beat,I replace decking on it all the time.The new treated stuff is pretty much a joke,I’ve seen it fail in less than ten years and sometimes as few as five with carpenter bees in it in less than a year.If the old frame is solid, I would put joist tape over it...
I’ve experienced that as well,just wait till Saturday or a holiday and get on with it. It’s nothing but a money grab,they want all the power and authority with zero responsibility for the finished product.
No inspector is going to let those slide without a engineers stamp.No engineer is ever going to give you one. You might possibly install new engineered trusses next to the old ones and then remove the existing ones but I can’t see the benefit to that.
A properly installed metal roof is probably the best option out there.I’ve made my living for thirty years going behind hacks and butchers and am still amazed at some of the sh t shows I’ve come across.