1) Yes, the pixel info not the text info. Unless you want the text as pixels.
2) Yes. For large memory allocations you should use the Photoshop memory suites.
3) Yes, but I would not open/write/close the currently open documents in Photoshop.
Look for ReadImageDocumentDesc *documentInfo in the ExportReocrd. Other plug-in types have a similar pointer. Filter, FileFormat that I know of. That pointer has a ReadLayerDesc *layersDescriptor which is a linked list to all the layers. The Poor Mans Type Tool filter example has some of this code as an example.
Yes, the documentation is lame. Please add some feedback here on exactly what you were looking for and did not find or other verbose feedback and maybe somebody from Adobe will finally listen.
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