To throw my 2c in as well:
I paid about the same as you are planning to spend on the whole kit for just my tent top from Trackabout. Now I'm sure they made money off the job, but I doubt it was enough for them to retire.
So when you are putting $8k of tent on top of a trailer, and charging $8k for it, the trailer can't be all that expensive, or the canvas has to be much cheaper.
Prior to my current setup, I had a locally made trailer with a chinese import tent top. The canvas was ok, and the top cost ~$2k with 3 annexes, but the number of poles required to set it all up was ridiculous. The most we ever set up was 2 annexes, and only when we had some friends camping in tents with us. A single annex plus a kids room is all anyone short of the Brady Bunch would need.
My vote would be to spend $6-7k on a secondhand camper, and save a few $ for any upgrades/extras you might want. A new kitchen, bike rack or tool box might be needed to bring a secondhand unit up to your required comfort level.
Regardless of what you buy, enjoy it. The worst investment is a camper trailer gathering cobwebs in the shed/driveway!