Hello. So, with the Warforged's Integrated Protection ability, I can integrate heavy armor into my body during a long rest, since I gain proficiency with heavy armor at level 1. When it is integrated, would it be argued that I could technically  gain the benefits of Soul of the Forge and Saint of Forge and Fire?

also would it be worth it to multi-class?

Integrated armor is armor that you are wearing, albeit in a special way.

So both abilities apply.

Ah, thank you very much Cube. I didn´t get the notification, so my bad that I couldn´t reply sooner. :)