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One room at a time is my motto, while you're in there making a mess etc. Depends how long you can live without a second throne room but I'd be addressing those walls cause you're polishing a turd with that lumpy plaster.
Find out how deep that old pipe goes, remove as much as possible and fill it with 4:1 cement, a browning plaster then a skim of something fine, Gtec Easyfill Xtra has been my friend this week.I levelled, boarded and plastered the bay window this weekend, not glossy smooth but I'm definitely getting better which means less time with the sander.
I'd be doing some plumbing too, that kink in the cistern tail would annoy me.