My last build went so far over budget though I'm hesitant.  

I was following James Dainard on biggerpockets and On the Market podcast for long time I was really impressed with skills and experience and successful journey.

I don't think it is any risk of collapsing.The driveway is about 80 ft long (garage is at back of property and driveway runs down side of house) and is one of those with grass down the middle with slabs either side. 

As long as they aren't staying every night and there are no parties or other concerning activities.

How long have they been there? 

Looking to buy a SFH in one of these counties, with the intent to convert a basement into an ADU and rent it out (short or long term) - and live in the main unit as owner-occupied.

From a cash flow perspective, you’d really need to think long and hard about the cost of leveraging these properties, especially in the current rate market.Yes a bigger purchase price might mean a greater potential of higher gross cash flow and appreciation, but that cash flow might get eroded fairly quickly if these moderate interest rates are here to stay.- REI CPA from CA

The last few I've sold in the area are around 6%.

But as long as they have a w-2 you will more than likely be able to collect.

Here in Reno, NV area the new construction has been appreciating faster that the market in the last 6 months.