AutoCad isn't really suitable for this kind of work. I used mostly Zbrush and Maya. 3d printer and 3D scanner 99.9999% of the times are 2 separated products. You can use the bed leveling system of a printer as a 3d scanner. but the resolution and axis range isn't great. So you need a separated 3D scanner. For small parts one of the best methos is structured light scanning.
The scanner good for this use would cost 2500 usd (https://www.conrad.com/p/david-sls-2-3d-scanner-1209136)
The printer is really cheap these days. Any SLA printer between 200-300 usd is enough (Elegoo mars or anycubic photon for example)
A last update on the colosseum before getting back to the characters.
Most of it is modeled, it's only missing the ornaments. Next step is to texture it and animate the lights, skydome etc.