I spend a while trying to figure out meshmixer, I ran into so many problems with it, it would not let me download objects either. I thought it would just be best to try and see what I can make with that I have access to on meshmisxer.
I was only able to make one assemblage before my computer decided it couldn’t handle meshmixer and wouldn’t let me access the application. I hope that tomorrow I can try restart and redownload meshmixer.
Looks like you were on the right track. Too bad about the computer speed. I have put up a tutorial on how to reduce polygon numbers. If your computer is struggling then working with smaller poly counts will make it eaiser.