The build cost would be a little higher because i would use foam in the exterior walls and also use insulation in the interior walls for energy saving and sound dampining.

Yes, it is possible to obtain a second FHA loan, but only under specific circumstances, as FHA loans are designed primarily for owner-occupied properties.

Sometimes minor tweaks to the design can garner their support which is far better than having an adversary. 

Advice on Layout/Design: For those who have added ADUs, do you recommend standalone units, garage conversions, or a combination of both?

I also renovated houses and own an interior design and renovation business. 

And don't forget to factor in design/furnishings into your budget keeping in mind your ideal guest avatar.    

We also made serious changes to the exterior entrances and decks.

BiggerPockets is full of resources designed to help you along your journey, whether you are just getting started or a seasoned investor.

You're making a fairly common mistake of designing your castle when you haven't even learned how to build a chicken coop.

Quick tips…✅ Everyday Homeowners - track all home improvements as you could qualify for energy efficiency home improvement credit - new exterior windows, new central A/C, new hot water heater, new insulation material.✅ Investors - Keep detailed records of ALL rental property expenses to reduce your taxable income - helping your CPA spot additional tax saving opportunities.Imperative to use a CPA who is well versed in Real Estate tax code.My CPA is just that - DM me to get his contact information....