8/10 oz canvas seems a bit light. Mine has 12 and 15oz or about 50% heavier. The quality of the waterproofing is more a result of treatment rather than the canvas.
The feeling I got from looking around was that a good quality CT without the extras will set you back $7000.
We got a 2.7 metre room which is ample but not too wide for a standard powered site at a caravan park, worth considering if you are going to do any travelling. A 2.4 metre room is probalby ok but I found it depends on where the door is. You need room for the ladder up to the bed etc, and if the door is at the end of the room you reduce your usable space. Our door is in the middle of front wall of the room, with bunk beds at the end and to the right of the door . We got bunk beds for our kids (now 3 and 5 and tied to one of the internal poles) to reduce the footprint.
With ours you now can get a 3.3 room but do you need it....
The plastic at the bottom of the windows. Well I like a dark tent so the kids don't wake up at 4:30am in the summer months. Thats only a problem for us daylight saving less queenslanders of course.