Lead was in the paint for giving the paint one coat coverage and wareability/toughness. If you scrap your finger nail or a wood stick over suspected lead based paint you will get a grey colored streak. this is a pretty good indicator that if for have small children around that will be putting small things in their mouths you should remove it or encapsulate it under a coat of the approved sealing paint and the at least one top coat.
One shot sign paint was called such because of the amount of lead is in the paint higher then the other brands. Before it was mandated to be removed. It would cover in one stroke when painting letters. Red was the paint with the greatest amount in it. You can always tell when a sign painter or wall dog used cheaper paint as the red is the first to go and only leave a slight trace behind. Followed by the other colors, in the days before the UV blockers were developed.
The one single difference you will find in using house paint compared to model paint or even craft paints or artists paints is the size of the pigment grinding and filler size. It will be a lot larger compared to the better model paint or artist paints in oil or acrylic, acrylic/latex. If you have a lot of details, deck plank spacing lines,bulkhead lines rivets or other lightly scored details. You will notice they fill up faster with the house paint. So you will need to enlarge the lines or do a number of thin coats. Problem with thinning the paint to much is you also thin the vehicle, pigment, binders,fillers and dryers that are added to the paints. Which can cause wear and adhesion problems along with coverage.
Any of the exterior paints will be water proof up to the approved thinning rate on the can. Whether oil or acrylic, acrylic/latex. Not for being submerged in water 24/7, but say if they are dried for a week and then used they should be set up and (dried) from the outside surface down to the layer up against wood, metal,plastic.
I'm not familiar what types are sold in China for household projects. But a better choice would be the kind of paint that is used on toys, furniture, and general use/decorating type.
These are the type of paint I'm referring to.
Here is something that can come in handy and save some mess when mixing paint. Battery operated drink mixers. One of the US model suppliers was selling the same thing for $9.99 but the picture had the cardboard display and I recognized it at the dollar store
From left to right Extenders two different brands thinners and will also thin the opaqueness of the paint. Thickener thickens the paint but a side effect is it also thins the opaqueness of the paint. Another bottle of just thinner for either brush or airbrush. Gesso is the thicker material that is like a primer for canvas or other material, wood, Masonite, metal prior to painting on it. Modeling paste is a thin material that can be mixed with the paint or painted over after it is hard. for mud, and rust or barnacle effect. The last is a lither version of the paste called a snow paste. It is used for winter and ice effects easier than using parrifin wax
Check out the artist supply houses or web sites, or your local craft big box stores as they are a treasure trove modeling supplies.