An Ultimate with the kids room would easily hold two adults and four kids; with the kids spread out between "upstairs" and "downstairs". The whole "upstairs" / "downstairs" set up is easily done within 5-10 minutes.
To answer the OP's questions ...
1. Which is better - Hard floor or soft floor. Had soft floor before and kids often grumbled about the surfaces that we camped on. Any thoughts appreciated. Am currently leaning toward the hard floor.
We went for hard floor. It just happend to be so and I am glad we did as we don't worry about the ground surface.
2. Which sort of camper would be good in a price range of around the $40,000 mark. May be able to put a bit more into this for the right camper. At the same time the cheaper the better.
I am biased, but Ultimate are good
3. Companies that we are currently thinking about are Hardfloor - Aussie Swag, Australian Off Road Campers or Cub or the Soft floor - Complete Campsite or Trackabout. Would be willing to hear about any others also. If any thoughts on these particular companies - good or bad would be appreciated.
Our Ultimate will be for sale in the next few weeks in the OP's budget - hint hint
When the kids are grown up, the Ulti is perfect for two people. Nevertheless, there are rails for attaching Rhino Rack bars for bikes etc, the CT itself is light (700 kg tare), has 110L of water and will follow you anywhere.
Just for something different, here are some photos of the configuration of our forthcoming camper. It will sleep two adults and four kids (we only have two). This isn't our camper, but are pics of what the CT manufacturer has done when they fit out two sets of bunks that can transform into couches -