Readymix screed is the way to go for bigger jobs. It has a retarder in it so doesn't go off for 24 hours.
It comes on a tipper lorry, not a Readymix type concrete lorry, as it's mixed at the plant, not in the lorry.
They just tip it all off in one go where you want, so have the area clean and clear and have tarpaulins to cover it (stops it drying in the wind and keeps rain off).
How you get it into the basement is up to you, you know the site layout. I've had to have it hodded upstairs before now
Every job is different
As it takes so long to go off, make sure nobody can access the floor (including cats etc). Turn off any heating, especially hot pipes to be within the screed.
Good luck!