House extension questions

I'm trying to find information on the basic process for a house extension...the house is currently 1100sq ft rectangle with a oversized one car garage on the front...I'm looking at tearing down the garage off the house and adding a 12w x 16l extension of the living room and a 22x28 2 car garage, within the garage dimensions would be a 5x7 bathroom.

I have the base design CAD'd out...checked the city building code for lot line setbacks and am good....assuming the design is close to final would the next step be meeting with an engineer and getting legit building plans?