I figure that almost all of our flooring is made in China anyway, so I'm wondering if I can cut out the various middlemen and buy directly from the manufacturer. 

I never really waste time with any captive shops since they can only do one thing to lower price which is lower the rebuild value.

My mortgage would go up $781 for the next 30years,  the ADU income would more than cover & I hope to pay extra principal to cut my loan time -it's just I was hoping to pay off ADU within 5.5yrs- so that I can collect 'all' ADU income at that point <I'm fixed income & I lose 'some' personal income in 5yrs so trying to plan ahead on how to recoup that>.

Yes, it can feel like "wasted" money on months where rent is auto-paid and there is no maintenance to be done, but when you get a bad tenant or two or when deferred maintenance finally catches up to you, they certainly earn their keep.At your scale, you might be able to get a bulk discount with a good PM, especially if you can show how well your current systems are working and how they'd be needed less than usual.

I have a wooden retention wall as attached which is about 30 year old I think from the time when this building was constructed, I have made slope down on right hand side corner last year for landscapers, tenants to go into ditch to cut the grass rather than leave it become mini forest with poison ivy plants as well there.

The worst ones usually don't have any clear cut guidelines (a lot of the underwriters will make up their own rules if they do not like the deal), Suck at communicating (will reply days later), Push aggressive terms to get deals in and then switch them, and Not really motivated to get things done (they will adverse a loan without any hesitation). 

After you find the list, are investors directly contacting the owners to cut a deal and buy the home before the tax sale?

If the sample(s) that tested over the threshold were from under a window (which is the norm), you probably need to address the window frame/sill and I'd recommend just cutting to the chase and painting them. 

I was initially told there was an HOA but eventually found out it's not active and there's a lady who lives somewhere on the street that pays a lawn company to cut and trim everyone's yard. 

It was a waste of time to try to even set up.