That game concept would definitely be possible. Q3D includes simple 3D collision detection but you're equally free to use invisible sprites for the underlying logic, and position the 3D objects based on those. I can say at this point the plugin is quite user friendly, but it's still a lot more complex than vanilla construct since you need to understand scene graphs / a different workflow.
There is no trial version. You can assume performance is equal to that of any current three.js examples/projects of comparable scope to what you want to achieve, the underlying engine is the same so the performance should be mostly equivalent in terms of rendering (logic depends on implementation).
I don't have any videos yet, and i know that's a turn off for many users. I plan to improve the plugin enough that no major changes will occur before I make videos, as having them go obsolete after putting a great deal of effort into them wouldn't be worth it. I'm thinking this will be after the next update in which I plan to include support for 3D physics and skeletal animation. This might realistically be out anywhere from 2-4 months from now, if you don't mind waiting potentially that long.
Other than that, i check the forums regularly, especially this thread, so feel free to ask as many questions as you wish!