It took me some effort to find this, and I’m not sure if it’s 100% relevant, but the technique I mentioned for (1) is in this post, although the PDF link seems to be dangling.
To save time in parallel runs (2) , be sure to share the ambient file if you are using -ab 1 or greater by specifying the same -af option for every rtrace invocation.
If you set rtrace -x 1 for judging doneness (3), it will send out every value as it’s calculated.