New leaves will generally be smaller than leaves at the base of the plant. Keeping your plant trimmed back will help the plant become bushier.
Brown spots could be water spots or even insect or disease damage.
If the spots increase or you see other signs of it spreading, treat the plant with Neem Oil. This works as both an insecticide and fungicide.
It's safe for people and pets.
Here is a link to refresh you on the care requirements.