My personal experience with Mi4i, It does have a medicore camera. with lack of IOS, u might wanna use a tripod to take pictures. However, its HHT and manual camera (pre and post processing) does help alot. I d suggest getting another camera phone, like Samsung's Note series, LG G series or Sony Z series. Or maybe Mi note?

In regards to over heating.. there has been alot of talks about it, mostly from warm climate countries. My Mi4i is still at 6.5.3 (one of the few version that does not have major heating issues), and i do not notice the heating issue. But maybe its because i work in a controlled environment of 16 Celsius and 20% humidity.

Also since u did mention travelling overseas, Mi4i have a good battery life so you should do fine. But if you do get another phone, try to get one with a good battery capacity.

Feel free to ask anything if u need more clarification.

if u die die must buy this phone, get the 32gb
dont forget memory is not upgradeable.

it lags, and it lags a lot  that is if you don't freeze its miui apps or go for cm