I don't much like Crosby personally but I think if this is a name you love you should go for it. I don't think people will think you named him because of this one character, the name is too common for that. August is a wonderful name. I don't think people will shorten it to Gus unless you or your husband do it. I don't think you need to worry about popularity as much as you do...certainly not into the 500's but check out the popularity of your state anyway, it can differ from the national. The SSA site has it all. Names that I think would go well with Maeve:
I love August it is our boy pick his NN could be Auggie as well as Gus. But I would call him by his name in front of other and just call him those cutsie names at home in private that might help cut down on others calling him that.
I love the nn Gus, but I prefer Angus to August. Rory is an adorable name, though I'm not sure it goes with Maeve. Crosby will forever remind me of the hockey great, Sidney Crosby, which is definitely not a bad thing.
Some other great Irish names:
Or, my personal favourite Irish surname:
Hmm how about Rafferty with Maeve? You also can't go wrong with August. Wishing you all the best!
I think you could get to Nn Rory with either Riordan or Ronan too.
If Declan (my far) is too popular where you are, Finn probably is too.
Also think maeve goes great with Henry, more classic.