@Alejandro GarciaInspections, due diligence on the property, decide if you are leaving as is or adding square footage, invite GC's and or subs to come in and quote for work at the same time as inspections so you aren't being rude to the occupant and respecting their time, invite architects if you are modifying anything, also invite them if you are converting the garage into an ADU, if you are terrible and design, find someone who isn't, most GC's are so don't rely on their sense of design.

You should talk to a builder or architect and see what options you have.

I had several people tell me that I'll need to hire an architect or zoning attorney to get this through.

Without a couple of licenses under you it is impossible to take notice by anyone,  Many architects carry PE license also with a more technical background.

Condo conversion legal fees are about 15k, architect/design fees 25k.

A bit biased as I'm a Solutions Architect there.

Then we will research potential partners on the ground- finance partners, realtors, contractors, handymen, lawyers, title companies, investing partners, architects, and property management. 

Wrapping up a new construction 7 unit in Los Angeles, mid way on a 5 unit new construction in Los Angeles, about to break ground on 5 units in Los Angeles, have a 7 unit building in plan check in Los Angeles, and working w architects on a 4 unit ground up town house project in Inglewood.  

(I suggest you still interview each team member even if referred by a great agent: ie Contractor, drafter, architect, lender, realtor ). 

Architects, engineers etc.Who will be liable for any debt or construction loans obtained?