As far as staging goes, take photos of each room now, and look carefully and critically in the photos for visible clutter. Sometimes you'll see stuff in a photo that you won't see with your naked eye.
Look under beds, on top of wardrobes, on counters, on chests of drawers, in bathrooms, stuff lying around in rooms, stuff that seems to be bursting out of its assigned space (toys, coats, stuffed animals), and office space that looks like a hurricane blew through it.
Start now to get rid of at least a quarter of what is now in your house - extra clothes, old footwear, outerwear you no longer use, kitchen stuff you never use, old toys.
Make sure nothing is visible poking out from under beds.
Put at least half of remaining toys and books into storage boxes - if you have a garage or garden shed, that might be a good place to stow storage boxes.
If there is children's play equipment in downstairs rooms (play kitchens, storage units, etc) move that out of sight either permanently until you sell or just for the day when the estate agent photos will be taken. Ditto high chairs, children's tables, art spaces in reception rooms. If you have a dedicated playroom, it's fine to leave stuff there.
Take down family photos and pack away.
Reduce knick knacks.
Check carpeting for stains and worn patches.
Make sure bedding is nice looking - pale duvets are a plus.
Make sure curtains or blinds are not dated or gloomy looking.
Make sure furniture isn't showing signs of destruction by animals or children.
Touching up paint is a good idea.
Power washing the drive and sprucing up the appearance of the front and back gardens is a good idea.
I'd maybe hold off on the chimney work.