According to what you describe, it seems that the number of images is probably the reason why the project does not open again.
Indeed, 492 images with 8 GB of RAM is very little.
Anyway, it would be good if you could send me the log file including the first process. I would like to have a look
I would also ask you to try to process with less demanding parameters, for example, 1/2 for “Image Scale”, less density in the point cloud… By doing that, the software will need less RAM.
As for your off topic question, there is no way to change the size of the tiles but you can merge all of the tiles together and get only one file. Just check the “Merge Tiles” option:
Please let me know if having less demanding settings helps.