Home/Remodel Extension recommendations

Not sure who to start with, do I need a Architect or Engineer first or are their General Contractors that have staff to do the design options?

I have a 1950's block house in the Milk district with a concrete block detached garage and I would like to expand the house to add a larger bathroom and main bedroom. I would also like to turn the garage into an ADU that will be used as an office for now.

Does anyone have recommendations on where to start or recommendations for a architect/contractor/engineer as first steps for seeing what my build out options are?