I may not be able to answer your specific questions but perhaps my limited experience may help.
These tools are not “click and print”, they require trial and error to get what you require.
I used lithophanemaker.com for a while but couldn’t get a decent quality colour print, blacks were coming out as blue. I tried to edit the picture to try and compensate but no luck. I managed to get in contact with the author of the colour tool in lithophanemaker.com and he informed that there are issues with the colour algorithm and that work is ongoing to try and correct. So for me I had reached a dead end with this software. For more information on this see my post:
Then gaugo posted his new software application which I have downloaded and tested, initial results are really encouraging, the software allows multiple filament colours to be used (not limited to 4 colours as lithophanemaker.com) to allow good colour detail. I am waiting on my second AMS and 0.2mm nozzle to print my results from PIXEstL.
I would encourage you to have a look at PIXEstL, once you get past the initial learning curve it is very easy to use and for me at the moment the results look good. Will post my results once I’m up and running.