I applied car sealant (https://goo.gl/KcipK3 amazon link, no affiliate) to my car. After that, I should use only water when washing my car? Or going normal car wash is fine?
(I mean, as long as the coat lasts, which should be 3 - 6 month.)
You can still use a car wash, however it's always better to lightly hand wash a car, and keep the automated car wash use to a minimum. As after years of car wash use you will likely start to notice brush rotation lines in the paintwork.
Agreed car washes have come on in recent years using softer brushes etc, but they still use filtered water and chemicals, so how often are these filters checked or changed, and who knows what chemicals are being used. Plus the brushes will likely contain grit particles from many previous dirty vehicles, and judging by the state of some of the off road vehicles that use car washes I'd hate to see what they looked like under a microscope.