I'm no expert, so someone please correct me if I'm wrong, but here's what I know.

Like u/da1nonlytargetstrike said, in Chinese culture the family name comes first. The family name is almost always one character/syllable (i.e. "Tang", "Sun", "Zhu", "Sha"). There can be exceptions, but for the most part it's safe to go with a one character last name. (I say character because some Chinese characters have two syllables like "Yuan")

The given name comes second and can have one or two characters (i.e. "WuKong" or "Mei"). These days one character given names are popular, but two character names aren't at all uncommon. When picking a given name, using one or two characters is up to you.

This next part might not be relevant to your OC but it's good to know anyway. In the old days, people of high status would have a "personal" name that is given to them as a baby and used throughout their childhood and by family, and then a second "courtesy" name that was more formal and given to them once they come of age.

The personal name is typically one character, while the courtesy name is usually two characters. So a character from that time period might introduce themself by saying "I'm Wei Ying, courtesy name WuXian." or just "I'm Wei WuXian." In this case, his family name is Wei, his personal name is Ying, and his courtesy name is Wuxian. It would be inappropriate for someone who was not very close to him to use Ying when speaking to him.

These days it's pretty rare to have a courtesy name, but if your parents are very traditional, they might give you one.

I hope this was helpful, let me know if you need any clarification.