Good luck. I personally dislike MassTransit as it's way too opinionated for what it does. I use whatever SDK I need for Azure Service Bus, Kafka etc. and perhaps slightly wrap it for my purposes.

As for the other bit around AutoMapper. I do my own mapping and so should you. MediatR and what it does you can implement yourself in a few hours that will cover 90% of use cases if you know what you're doing.

All in all I want less dependencies in my code. Everything is bloated to shit anyways.