My 1yr, 3.5 lb, white long haired chi used to have his puppy coat but with a neuter his coat soon thinned. ?

He had the most adorable freckles which in time multiplied and soon his body has them all over his body. You can see them through his fur. My first question is in regards to the loss of hair. I have been told it's everything from a hormonal change from his neuter to it's due to the adolescent stage in his life. Sort of an ugly duckling phase. I've read you shouldn't neuter until they reach at least 18 months. Should I be concerned? The next question is about the pigment change on his skin. He used to have a few dark freckles on his belly but now almost the whole belly is covered and he has them scattered throughout his entire body. I use dog sunscreen if he is going to be in the sun for long periods of time because he's so fair. So is this change also normal for a pup going through his adolescence?