Service life of iron and copper: 80 year old house

I am embarking on a full kitchen renovation soon, and there are a couple questions I have not been able to find good answers for on the internet. I figured I would ask them here, after using this site as a resource for years, I finally have a reason to register!

My reno will start with a full gut out, exposing most of the 80 year old (1936) cast iron waste stack and the bottom side of the bathroom above. The waste stack continues through the bathroom wall, and is exposed in the large walk up attic, before it penetrates the roof. I am planning to replace this whole stack, bathroom wye, and WC drain (terminology??). There are pinhole leaks in a wye in the basement, and I'm assuming other parts of the stack will not survive past the next time it would be desirable to take down walls and ceiling in the kitchen. I'm planning on replacing with pvc and insulating sound with mineral wool and extra drywall, and planning to hire a plumber to do the stack replacement, as it is heavy and I don't want to deal with it. Am I on the right track here, or if say everything appears to be in good condition, could I expect another 30 years out of it? I also believe a replaced cast iron stack will increase value in a sale, which is a real possibility in 2-5 years.

Also exposed will be perhaps 30 year old copper supplies to the bathroom. I am debating whether or not to replace these. I can do these myself, so really the only cost would be materials. Complicating this is the possibility of using pex.

And finally, something I haven't been able to find any information on, and perhaps more appropriate for the boiler forum, is the 80 year old iron hot water radiator supply and return lines, which will be exposed for the bedroom and bathroom above. What's the expected lifespan on these? Should I worry about replacing these if they show no sign of leakage or corrosion? I was looking into replacing these with ox barrier pex, but it really seems like a crapshoot as to what would last longer, brand new pex or old iron. Perhaps new black iron? Again, I am capable of replacing this piping, so really the only investment would be materials and time.

Thanks for any insight you might have. I'm looking to do the job right, but open to the idea that the right thing might be to not fix what's not broken.

If you have the walls open, I like the idea of replacing the waste lines.
They do tend to rust out on the bottom of the pipes.

The copper should have more life in them for the water supply. Though if they get in your way while changing out the waste and vent, it's not a big deal to remove that too.
If you are opening up the tub and shower area, replace the valves at this time.

Thanks for the reply. I'm somewhat worried about the waste line, I had redone the stucco on the wall where the stack is, and i remember the sheathing was cut out in places for the hubs of the waste stack to fit. I'm hoping the whole stack can be removed from the third and first floors without damaging the second floor interior wall, but if the hubs are locked into the sheathing I can see that being a challenge. I have posted my radiator question in the boiler forum.