Running multiple effects in a single via is not forbidden nor wrong, but it defeats the purpose of Missionary. A blackbox is not desirable if you have a way to define, compose, and run effects the right way at hand.

I wrapped the http call into a task, does it need to be also be wrapped in a (via blk http-task) ?

Is your http call a blocking operation? If yes then via seems appropriate. Also, via returns a task, so no need to wrap you http call twice.