Yes designing is the easy part for me since I do that all the time. The above model is 5 minutes to make once I measured the original part. There is also 1000's of models you can down load from https://www.thingiverse.com/
The print time varies so much based on your setting. The prints are not 100% solid. You decide how thick the outer layers are and how dense the inner honey comb is. On my center I did 1.2 MM thick wall and 50% honey comb. That was about 8 hours and 11 meters of 1.75 MM PLA plastic. Drop the honey comb to 35% it might drop the time 20 minutes. Drop the shell to .8MM it could drop the time an hour. You also set the print speed. Slower = better. For mechanical thing you need stronger, My son in-law was excited because he can print his D&D guys with the correct armor and weapons. LOL I am not burning a lot of plastic for that.
I posted the link for the machine above. It is a 8" X 8" X 7" machine.
Software is VERY easy to use. Open your model, rotate is around and move it where you want it, start with the default settings and you are 95% there. When you buy the above printer it ships with the Cura software already setup for this machine so most of the settings in the below video come already set.