- The camera does not support USB "mass storage protocol"
Not sure what your point is. No remotely recent powershots do, and CHDK does not change this.
- I use a 8 GB SDHC Card (preformatted with fat32) which is identified with "7.9 GB" (setup menu, formatting option). Have not filled her up yet, so I don't know what happens after 4 GB.
Normal 1024 vs 1000 inconsistency, and FAT32 supports over 4gb, so nothing special should happen.
- Since I don't have a SDHC/USB device I have formatted a 1 GB SD card with fat16 and set the bootable flag, so this is where CHDK runs from.
Set the bootable flag how ? The canon bootable flag is not standard.
- Instructions in the WIKI and in distributed install.txt are inconsistant and did not apply to my case. "update firmware" has moved up a menu level and seemed necessary to run CHDK.
If you want the wiki to be clarified, please specify which particular instructions you are talking about. Similarly, if there's a section of the install.txt you find confusing or incorrect, please specify which one.
- make bootable should be explained to just set the boot flag of the memory card's partition
No it should not, since that isn't what it does.
- How exactly does CHDK "overlay" the DryOS functionality? I mean basically this is not new firmware, but just an additional level !?
- How does the autoboot-on-card-lock feature work without changing the original firmware?
It's loaded into memory, either when you do the "firm update" with a CHDK fir/fi2 file, or at boot time if you have the bootable flag set correctly and diskboot.bin in place. In either case, it performs a modified version of the canon startup which mostly reuses the canon code, but adds our own stuff at key points.
As for the optical zoom in video, either it's not correctly implemented for that camera, or you are doing something wrong