I don't think it's stupid at all, it seems like you have a purpose for both of them so I'd go for it! I would get the messenger bag first since it sounds like you would be using it more than a keepall. You can always save for the keepall and get it in a while, when you think you may be doing more traveling. Hope to see a reveal of your new LV messenger bag soon!
I honestly don't think there is anything wrong with having two! If you wear both, and they are different bags, go for it ! It's nice to switch it up a bit.