It looks like I am facing the following jobs:
- timing belt
- 'de-sludge'
- AC not cold

Which, if any, does it make sense to combine while at it?

 

you could throw a can of freon at the ac and see if it sticks, but with older cars it's usually leaking. You would need a shop to inject an infrared dye into the system and find the leak.

The other two would be a solid weekend.

I'm curious how well the de-sludging works, to me the whole idea of an oil starved motor is scary, even if you can fix what starved it in the first place.