If you’re set on a duplex with minimal rehab, an investor focused agent should have a strong network of contractors who can give you quick quotes, so you don’t wind up with any pricey surprises.

The buildings were still usable.  

Educate yourself with books, podcasts, and market research, define your goals, and build a team of professionals to support your journey.

.: Hello All, I'm interested in building a Mobile Home Park on some property I have in Texas. 

The idea is to convert a multi-family building into condos; but not in the traditional sense where you separate pre-existing apartments into their own condos; but in a way where you combine the common areas of all of the apartments in that whole building, and turn the individual rooms within those apartments into condos themselves; thus transforming the hallways, kitchens, bathrooms, living rooms, dining rooms, porches, balconies into common areas of the condos. 

When I was tracking my hours, I used WhatsApp to communicate with my property manager, contractors, and guests—it timestamped every conversation and became my built-in log for documentation.

For example, I own two large multifamily buildings, and when I tried to get a tax exemption for them, I had different experiences.

Just in case.Ultimately whatever correlates with your future plans but a solid way to build long term wealth.

Also you seem to be motivated to build since you already have these lots. 

And your net worth will thank you.If you still want to go ahead, you'd be better off buying a house than an apartment because, while the value of the building itself will go to 0, you'll still have the value of the land, bearing in mind that the land might actually lose value too given the depopulation and the yen depreciation.Sorry if I'm pooping a party but make sure you understand what you're getting into (which you're already doing by asking the forum) and then make the decision that's right for you according to your objectives.