Before I answer, I need to say, VOIPAC Baseboard is not our design. So I am not sure why they did some things.
1) I use Solid
2) These are not necessary. I used to use them, but do not do it anymore. It was helpful to check if PCB manufacturer placed all the layers into stackup correctly.
3) Voipac designs are not our boards, so I can not really comment about this. It depends on the engineer. For our designs, we normally try to clear all the errors. if you like, you can download examples of our designs at
http://www.imx6rex.com/ For the Voipac design, if you like, you can try to correct the errors, you can learn from them or you can ignore them. We will be speaking about some of the things during the course.
4) Very often we have Overlay touching each other. If you are doing placement this way (overlay is touching each other), be sure the real component is always smaller, so it will be possible to fit them.
5) Again, this is not our design. I am not really sure why and how the designer created the layers - we normally do it differently.
6) I normally try to avoid this. If possible, correct your PCB. Normally this may be removed by PCB manufacturer, but some manufacturers will not remove it and then it may affect soldering.
7) In our company we use a server. We map folders of this server to our local network. All people work directly with files on the server hardrive. And ... on the server we run the google drive app which is synchronizing and backing up the files from server to our google drive. This way it works oki (even if google drive sync stops working or is delayed)
I hope this helps