Do you decorate room or strip floorboards first?

Re the gaps .Do you have any old boards that you could slice up and glue/tap in to the biggest gaps .?

Do really need the advice of that questions?

If so...do you mind getting dust on a fresh coat of paint on the walls and ceiling?

I'd decorate first, any spots of paint will come off with the sander. Other way round all you have to do is vac up the wood dust.

Depends on traffic and the apearance you want. Two packs are the most wear resistant. Check out

Never had much faith in the PVA/Sawdust mixture method myself. You could cut tapered strips on a table saw, glue them in & plane/sand them flush, or lift all the boards and use a floorboard cramp to relay the boards with no gaps. This would leave a gap at one side equal to the sum of all the small gaps.

This caould be filled with a scribed board, or if you have pipes along one wall, covered by boxing them in.

One assumes the OP is bright enough to allow the paint to dry completely?

One assumes the OP is bright enough to put paint sheets down after sanding the floor and leaving the varnishing/staining of the floorboards last.

Surely only a fool would sand floorboards while the freshly decorated room had wet paint?

Always decorate top down. Ceilings, then coving, then walls, then skirting (and other gloss) and floor last. I'd recommend covering the floor while painting the room even though sanding will probably remove the inevitable paint drips.

Solvent based have a yellow tint and water based acrylics are more dull and cloudy. Worth putting up with the fumes and destruction of the planet

Once the floors have been stripped treat them as soon as possible, if left untreated any stains left by spills etc will be almost impossible to remove