I would highly recommend that you work with someone that has experience with the wM product suite, if you don’t have someone on your team already. SAG consulting services or some other group that you can contract with to help would be highly advisable. If you have no exposure to wM before this project, you’ll be diving into the deep end of the pool. You likely want a buddy to help you swim. 
I imagine the desire to replace UM with Kafka is price-driven. Be aware of the tradeoffs. If you go with Kafka you’ll use JMS and would have a lot more administrative tasks than with UM. Additionally, per this article you can’t use JMS triggers in Integration Server to receive messages, likely increasing the coding complexity.
With the IS and UM combination, you don’t have to do much of anything in terms of managing topics/queues etc. When you define a publishable doc type on IS, it automatically configures UM. When a new trigger is defined, IS automatically configures the topic/queue on UM. Using Kafka, you get to do all that manually.
As usual, its a trade-off of cost vs time/complexity.