I'm about your height and weigh in at 180.
Now saying that, i also can get up to 190 (after holidays 12¿) and drop down to 170 (when i train for tournaments and get to 9¿). That is my comfort weight range. Everyone has different comfort weights. I really don't look at my weight anymore but look at my body fat percentage. Again, this is me - NOT YOU.
When should you stop loosing - when you feel like you should. Your body, program and diet will tell you where you should stop.
My diet, cardio, water polo and weight traning keeps me at my comfort level. You will evenually feel like you can relax your diet a little (note the little) but to maintain your weight you will always have to watch what you eat because as men age, our metabolism slows and it gets easier to gain fat when we don't excercise.
The short answer is - when you feel like you should.
But also be carefull about unrealistic expectations. We all suffer from the adonis complex. We all can't look like the fitness models. Some of them are "chemically enhanced". I don't recommend that route.