I'm concerned that the combined load of heat pumps and ancillary heat strips, along with other appliances, might exceed the 100-amp capacity during winter.As part of our future plans to add a third unit and separate the utilities, we intend to install two additional meters: one for common areas and one for the new unit.

Installed dedicated app.

So give another 12h notice to the tenant, drive there again and install. 

You could potentially install a mini split for the downstairs unit so they can control it themselves but that's a more costly remodel.

The exterior we removed all sheeting and replaced everything and installed vinyl to update it.

You just paid more than buying a washer and dryer with delivery an installation.

Consider an Installment Sale: By structuring the sale to receive payments over multiple years, you can spread the capital gains tax liability over time, potentially keeping you in a lower tax bracket each year.11.

.$69.99 eufy SoloCam S220 Solar Powered - https://www.amazon.com/eufy-Security-Continuous-Resolution-C...We did buy these for the rental but I haven't installed them.

We started seeing savings immediately after the installation.  

If you choose to sell, consider post-retirement timing, installment sales, or a 1031 exchange to mitigate taxes.