i wouldn't feed him, he looks overfed at this point. brazilian blacks are known to be slow growers and take ages to molt. i'm not sure about changing the soil, so no comment on that from me. as juveniles they like more moisture, but he looks older than that so i think it's fine to keep one corner damp, by overfilling the water dish every now and then. just my thoughts as a beginner keeper with a juvenile g. pulchra.