It wouldn’t hurt to start that way they get used of doing it, but I would put any toothpaste on it you can pretend you do.

They say you should brush as soon as the first one is visible. It can be with water or non fluoride baby toothpaste ( I use Milk non fluoride by michael klim) just to remove the plaque from any food or the milk sugars

You should be brushing them now.

I would start with a baby set of brushes as soon as he gets his first tooth starting early is great