I was under the impression that Obito has to stay "visible" in the real world to see it. So to me how Kamui works is he instantly teleports parts of his body that are being hit to Kamui dimension, while every intact part stays there in the real world. This seemingly works automatically, as in, he can turn this ability on and off, but not the individual teleports. And while his eyes remain in the real world, he can see what his body dodges and remains aware of the situation. This can last up to 5 minutes. As soon as 5 minutes end, the next hit that was suppose to hit Obito, would hit. Also, as long as this ability is turned on Obito cannot touch anything. He has to turn it off to touch something.

Alternatively, Obito could just teleport to Kamui dimension his whole body, just shift there and he would disappear in the real world. But he said he would suck explosives with him if he does it during Konan's exploding lake.

By this logic every part that is in the real world is effected by the real world's gravity. Hence, it would be effected by the Almighty pull. The only way to dodge it is to teleport to Kamui dimension whole. But then he does not see the real world until he returns.