This option will allow you to take your time to really architect your plan that is in line with your long term goals and short term needs. 

The house is in need of serious repairs and as it sits, my educated guess ( Based on property tax values of comps and the fact that the same architect built 3 similart homes and his neighbor sold his house a year ago for $2.8 Million) its worth $1.5 Million or so.

I am looking for an investor with access to $1 million to pay for the architect and engineering and legal and finance work.

Let someone else hire designer, architect, contractors and achieve for value add. 

If you are moving walls around and need a higher level of service than those provide, feel free to send me a pm as I'm a licensed architect and live nearby.Good Luck,Mike

Can anyone around Nashville recommend a local architect for a house plan?

find out if zoning will permit what you want to do.Get a architect who has done this work in the city you want to do the work.

So do you recommend I reach out to an architect with ADU experience now before I find a property and clear my plan with them?

Just look at some of the more prominent members here and you will find out that the ones who are on BP almost everyday, and who are engaging in conversations, are the very same ones who do well in RE.

There should be a residential/commercial designer in your area, usually the offer drafting services, look for a draftsman first, not an architect but you may need one to modify a commercial building in your area.