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

Views, location to attractions and layout of property can make or break you in a good location or not so great location.

Layout is important.Not sure what this question is, but yes, you can typically sell properties vacant or occupied, or partially occupied.  

I made the layout more user friendly, added a whole wall of closets in the main bedroom, totally gutted kitchen and bath.

However, I have helped a couple people with extremely basic home layouts when they were in the process of remodeling their home.

This is where real estate investing turns into a great area and on paper investment strategies seem great, but when applying them to reality, things can quickly change.

There are many options, so instead of me listing a million things, it would be more helpful if you could lay out a few options you're considering, and I can provide some feedback from there.

Quote from @Mary Jo Carruthers: I have seen houses where folks did it anyways without the permit but that is really value destroying as it will make it very unlikely to sell for top dollar with that layout. 

It's a former adult care home, so the layout is shared bathrooms, and this would allow me to not have to change the plumbing layout while offering a competitive price-point and unique experience to travelers.

In fact if you don't do proper due diligence some are "traps" with bad layouts, fire damage, and tiny sized lots.