AutoCad stated a kind of standard that is followed by many softwares. Complexity and power are the only differences.
The more general and powerful is AutoCad.
For the complexity required here, and if you have to start learning a new CAD program, Im for Draftsight.
It's free, it can work with almost all standard files, and the layouts, screens, sentences and workflow are almost the same than in AutoCad. It can be taken as a simple version of Autocad and a good first step for learning.
DXF files do not grant measurements and hence neither scales. Its a general interchange file, 2D almost all times,(not reliable for 3D) that depending on the sofware were are imported, may change its size.
Native AutoCad files have .DWG extension. Those files include the whole information from the original drawing, including scales and measurements.
Anyway, from my experience, the only way to be sure about sizes, is measuring on the drawing a known lenght and comparing results.
Including that inforrmation (A reference line lenght) is always a good practice when exporting-importing any CAD file from-to different softwares.
AutoCad and similar softwares, apply thickness by extruding a base plan. The DXF files provided at GitHub, do not include this information, but only 2D plans suitable for cutting machines.
The way to get that information is by carefully reading the step by step, building instructions, and material lists from OpenRov. At those places thickness is referenced for parts identification.