Ok first, we don't know how he got it, but Madara didn't look so surprised when he saw it. This means there are other ways (harder, or takes a lot of time or who knows what) to get MS.
Second we don't know if he will get blind because he is not an Uchiha and things change in this situation. He doesn't seem to have any signs of blindness because his MS jutsu, Kamui requires a lot of concentration and focus on one single point, and he hasn't showed any difficulties in using it, by any means, he got better at it.
Third, you get EMS by transplanting another MS eye... So to clear things up , Kakashi has MS (mangekyou sharingan) not EMS (eternal mangekyou sharingan).