A few things @Raj Sidharthan - You should carry builders risk insurance and may be required to if you are financing the build.
Schedule all of your activities from start to finish before you start the job. Talk to your subs to get their durations to input in your schedule. Ask each sub what needs to be completed on site before they show up. They should appreciate this question.
Your local municipality will need to come out and do various inspections. When you go for permitting, you can ask them to provide you a list of needed inspections based on your build. This will help verify that things are being done correctly. Sadly though, I've done plenty of jobs where inspectors don't look at much.
If you really want to ensure the work is done right, you can hire a third party inspector but this can get costly.
Can you clarify on what "rough finish" means? Framing, roof, windows/doors, drywall, HVAC, plumbing and electrical complete? The remaining interior trim, painting, cabinets/counters, flooring/tile, and landscaping typically run about 30% of the project cost on my residential jobs.
All in all I say go for it if you are feel you are ready for it. Get ready to deal with the headaches of subs that don't answer calls, show up on time, materials getting delivered at the wrong time, incorrect materials getting delivered, not all of the materials getting delivered, dealing with inspections office, etc. Its a pain and GC's get paid to take that load off of you.
Also realize that the smaller you build the higher $/sf cost it will be. I can build you a decent 2,500sf house for $225/sf but that 425sf ADU might run $350-$400. <-This is still well below what you are being quoted but I'm not in CA either.
