You can thin certain water based paints with lacquer thinner, but I do not recommend you use lacquer thinner with it. I've experimented with that to get that extra bite on the plastic but it's not worth the trouble. If you are brush painting then just thin with water, especially since you are using it as a wash.
The problem with brush painting with Tamiya acrylic is that the paint will lift a previous layer. You have to wait for the first layer to cure before brushing a second layer or try to brush the base coat in one try.
There shouldn't be any problems using Tamiya as a wash over the Mr. Color lacquer. I assume you are in Asia somewhere. Model Master Acryl and Polly Scale are both very easy to brush paint with, but are probably not easy to find in Asia.