Mild Steel Plate for Steel Building Structure

I am a pre-fabricated steel building manufacturer. Normally I use ASTM A-572 Grade 50 Mild Steel Plate (Thickness: 4mm~16mm) for making Steel Column, Beam, Rafter by doing manual Arc Welding.
I am interested about the material jis ss400 because of its low price. I think its a low grade material.
I just see that the mechanical properties of jis ss400 is almost same to ASTM A36.
As per JIS G 3101 (ss400), Carbon (C), Silicon (Si) and Manganese (Mn) content are not controlled. Phosphorus (P) 0.05% Max and Sulphur (S) 0.05% Max have to controlled below these levels.... found in internet.
So far i know that if the carbon content increases, then the weldability decreases.

Hence, considering this fact, since the above mentioned material has insignificant carbon content, does that mean that this material has a very good weldability?

What is the weldability if compared to ASTM A572 grade 50?
Should i use this ss400 mild steel plate for making H-beam, column rafter by manual arc welding?
Please advice.