I just watched Iron Man 3, so hearing Stark just makes me think of Tony Stark!
I think the only reservation I have on stark are its definitions (1. rigid in or as if in death; 2. rigidly conforming; 3. archaic, strong, robust; 4. utter, sheer; etc). I think number 3 could definitely be a nice meaning, being strong and robust. The other ones do throw me off a bit.. thats just personal though
I think Benjamin Stark
has a wonderful flow, and its real handsome sounding! Benjamin is a super handsome name.. I really love <3
I think I answered the questions in my paragraph there lol or at least the first two :') The name as a whole sounds wonderful! Just perfect flow. And on Stark itself.. yeah. I think it works because its a middle name honestly! Creativity in the middle
And honestly, lots of names have less than positive meanings (Cameron's "crooked nose" and Temperance is "abstinence from alcoholic drink / moderation in eating and drinking" lol). And I can kinda see it working. Caia, Magnus, and Benjamin are all very strong names in my opinion so they fit in that thought. Benjamins a bit longer but doesn't clash.
Hope this helps!!