It is always better to finish a project in the program in which it was created.
But, you should be able in many instances to open a Premiere Elements 8.0/8.0.1 project in Premiere Elements 12.
The last one, topo_frame.tga, is easily explained. Premiere Elements 11 and 12 do not support .tga files. The .tga needs to be converted to .png for it to be supported in 11 and 12. But, that one is part of a Title Templates series and much has been written about that here and in my blog posts.
If the missing media message "Where is the file.....?" cites a certain file, then you need to find the exact file not one that almost has the same name and file extension.
I suspect you ran into much of your problems because, after you saved/closed your Premiere Elements 8.0/8.0.1 projects, you moved or deleted the source media that went into those projects. Those media disconnect problems are best resolved using the "Where is the file...?" messages, but can also be done with the Replace Footage feature.
So to answer your question
How do I bring forward my old video projects into v12?
1. Do not move the source media that went into Premiere Elements 8.0/8.0.1 after you save/close those projects, use the Project Archiver before moving source media, or be prepared for a lot of media reconnecting.
2. Be aware of formats from 8.0/8.0.1 that are no longer supported in later versions, example, tga.
Please review and then let us know if you have further questions or need clarification on anything written.