Looking at the Resene site, I see they recommend the pigment sealer for old yellowed plasterboard to prevent staining. I think I'll give the waterbased system a go.. and cross my fingers.

I have used a hand sander for one wall previously. It was new gib and the finish came up fine. Although it was a small area, still ended up with a ton of dust. Really keen to see if I can get some kind of vacuum system. I see a hand sanding, vacuum attached system in the above link, which might be interesting to try..

https://besttradetools.co.nz/collections/drywall-interior-plastering-hand-tools-accessories-sanders/products/hyde-drywall-vacuum-hand-sander-kit