Building an additional separate appartment in my house

[German Buendia]

Hello,

I recently bought a 3bd, 3full bathrooms house in Temecula with a bonus room or study on the 1st floor.  The layout is such that on paper I could redesign the bonus room, the downstairs bathroom and part of the 3 car garage into a small apartment/studio with all amenities inside my house.

Any suggestions on how I could dig more into this? I am new to Temecula and California. Will I need to get state permits or HOA permits for this type of remodeling?

Any help or guidance is greatly appreciated.