I always do a tb.stop() followed by a tb.wait(), because I assume that .stop() is not blocking but .wait() is blocking
Yes, this is correct.
If you call stop() then wait() you stop the flow graph and wait for the threads to actually shut down after they are commanded to. If you call wait() then stop() then you also wait for the flow graph to finish its work rather than stopping it early.
and this is the best practice way to prematurely stop a flowgraph. Or is the .wait() necessary?
You must call wait() if you want to call start() again, or if you want to wait for the threads to actually stop (which blocks may react to by releasing resources or other cleanup actions).
In my programming I make a habit of always calling stop() and wait() together, in whichever order suits the application.