Most kids go through the "my mommy" phase for a week or two no matter the gender. As young as he is he'll adapt fast, just encourage bonding, and special time for each.
My kids are exactly 18 months apart. My son has always been so sweet to his little sister and knew to be careful around her when she was a newborn. Just need to explain to him to be careful around the baby.
@the_yellaone, consider taking him to a behavioral therapist. That’s concerning. It’s normal that be worried about toddlers being rough but to be violent with intent is different.