I think this is very doable and indeed the capability exists now.
Input 1 (information about reviewers) comes from the spreadsheet download of profile info from spreadsheet maker
Input 2 (information about papers) comes from the spreadsheet download of submission info from spreadsheet maker
Input 3 (information about COIs) also comes from the spreadsheet download of submission info (?)
Output 1 (how to input reviewer assignments): if the code Graham is writing outputs in format: paper number:reviewer1startid;reviewer2startid;reviewer3startid that can be pasted directly into START as it is one of the three supported methods for providing reviewer assignment info.
It will be necessary for the scripts to be able to ingest information from START, and output information that can be ingested into START.