I opened a thai bank account with a 1000 baht cash deposit. You dont need a lot. Then you can do Internet banking to do any large deposits therefore not needing to carry large amounts of cash.
Can you not upload multiple files? I'm pretty sure the visa application (albeit not a retirement visa) allowed multiple files to be uploaded. If that is the case then name them xxx1.pdf, xxxx2.pdf etc.
Other than that there is software out there to merge separate scans into 1 document - Google search will show you.
AXA thailand but never had to use it in anger. Ts and Cs looked ok. As others have said Luma sounds pretty good so I may investigate them for my next visit.