You can start to add small amounts of salt (half the amount you add for yourself) and you can add half teaspoon of butter or ghee to food like khichdi. At 13 months many babies don't walk. If he is crawling fast and standing with support he will walk by the age of 15 months. This is normal.
As regards using curd for bathing I would suggest you use a mild moisturising soap only on areas like the armpits or the diaper area where it may be necessary. If the skin is dry add a spoonfull of baby oil to the bath water to prevent dryness. Using curd especially in humid weather may predispose to skin infections or allergies.