100k requests being free is an odd flex. You could do 100K of these in a few seconds on a free tier AWS ec2 instance.
Clickhouse says the minimum amount of RAM it needs is 8gb. Kafka also needs multiple GB of ram. How small an instance will you get away with?
To say, "I can run a server that can handle a bunch of requests for free" doesn't mean much. Of course you can do that. But can you replicate the aforementioned system for free? Probably not.
I wouldn't choose kafka for this setup as you could just use ch for everything