For those the 3rd grade can be better. So I think that 1,2 grade optional and from 3 obligatory is suitable.
I agree. The student should be able to fully grasp their own language before introducing another. It's a different kettle of fish when the child grows up multilingual, of course.
I've seen instances where English is taught in Kindergarten. I don't think it has to be detrimental, but I also don't believe that it makes a big difference in the over all learning process. 3rd grade is definitely suitable for all; any earlier instances should be dependent on the individual child.