Well, for Madrigal Book 7 I made a transcription from the Malipiero edition some time ago, which is available on the net as well, https://github.com/bjoerns/monteverdi
. Furthermore, I already transcribed quite some works from Renaissance/Early Baroque part book, so in principle I know which problems will turn up and how to solve them.
By critical edition I meant basically that all the changes that occur in the transcription process are documented somewhere... so far I did this directly as comments in the lilypond files, where most of the people won't notice them, probably not the best solution. Other questions that came up to me are then how to deal with the language part.... as my Italian is not really good, so far I decided to keep the spelling from the original, even if it differs between different parts (I only wrote out things like % indicating a repetition and short forms that indicate a doubling of letters).
Concerning Gesualdo vs. Monteverdi, I think that actually Gesualdo might be easier to transcribe, because his madrigals exist in a partitura edition so at least all bars from the different parts will fit nicely together.