When is it a good time to start building muscle
I would recommend continuing to lose weight until you are happy with the weight you are at. With that, if you are not currently lifting weights I would suggest you do that now as you lose the last of the weight you were looking to. It will also make your weight loss easier as you start to build more muscle.
I second this fwiw
Do both! I've done alot of research on building muscles and other things related to fitness along with nutrition and supplements. What I would really recommend is to head over to bodybuilding.com and read an article or two on losing weight. They will answer more than all your questions and they often include workout program ideas templates or even full programs. Tomorrow you go lift some weights. Look at some videoes of easy excersises like curls and rope variations. Give it a days rest if you're too sore to do cardio the following day. Mix and match here. I wouldn't recommend doing heavy lifting after a solid 50 minutes on the treadmill and another 30 minutes on the bicycle. So again, mix and match in days, not sessions on the same day.
Lifting weights does not make you lose fat, ever. Cardio and diets does.
the body doesn't know if you're burning calories by running or lifting weights. a calorie burned is a calorie burned.
the more muscle you have, the more calories it takes to maintain it (meaning you burn more , thereby losing weight)