i am using a 12000btu one for my 2xx sq ft bed room, it works ok. on the hotness days last years, it took 1+ hr to just cool down the room, so i think the 8000btu is kind of weak.
I had it for 3+ yrs, but don't need to pour water. if your a/c is not place close to window, you can buy the aluminum tube to solve the venting problem.
we have three bedrooms on upstairs, but we are only allow to put two portable a/c, otherwise we will get short circuit. so check it out first.