A. After graduating from college, I got a job in Kobe as a computer engineer.
B. I got a job in Kobe as a computer engineer after graduating from college.
C. I got a job in Kobe as a computer engineer after I graduated from college.
A, B, and C are correct. C is better than B. (B is very "Japanglish".) It is important to note that A and C have different meanings,
and this difference must be explained to the students. (Japanese students tend to always use the A example and ignore the C example, which is a mistake.)
I'd like to use "these days".
Yes, you can use it, but it is a direct translation of 最近 and sounds like "Japanglish". It is better to use the phrase "used to". "The number of Japanese students who go abroad to study is decreasing these days" is very "Japanglish" for a couple of reasons. First, "is" should be replaced with "has been", as in "The number of Japanese students who go abroad to study has been decreasing these days." (I teach the students to always use 現在完了形 with "these days".) But it still sounds very "Japanglish". Better to say "The number of Japanese students who go abroad to study has been decreasing recently." But it is best to say "used to".
It is natural for the students to want to use the direct translation of 最近, but this should be avoided, because this is not what native speakers say.