Are these two sentences correct? 1. 제가 쿠키 누구 먹었어요? 2. 제 쿠키 누가 먹었어요? Also, are particles used properly to indicate that: 1. "Who ate MY cookies" and 2. "WHO ate my cookies" ?

Is learning two or three languages at once a bad idea? Has anyone experienced this and succeed/failed? I recently got interested in Korean language, while constantly (but slowly) absorbing Japanese, now studying both more seriously. Considering that English is not my native language, I'm technically learning it too, on everyday basis. So now I find myself studying three languages, including getting used to two completely new writing systems. I'm asking because I've come across comments like "lol you shouldn't learn two (or more) new languages at the same time". So what's in your opinion or experience more efficient: trying to grab one by one or there's nothing wrong with showering myself with loads of different informations?