You may want a separate spreadsheet for personal tracking, but that depends on what you are trying to accomplish. 

Invest in a stock or fund with a huge upside on appreciation (think AI / Robotics).

I discovered that it is not uncommon for Caribbean homes to have separate living quarters, which gave me an idea.  

I'm new to BP, but have been listening to the podcasts for a while now and I definitely think it would be beneficial to separate out the regions and key words as there seems to be a lot of chatter about Rochester on here!

I recognize that creating an separate LLC for each unit would provide the most protection but that would create a lot of administration on my part.

Here's a breakdown based on your examples:Carpet, Vinyl Flooring, New Toilet, New Vanity, New Tub: These items are typically considered assets because they are permanent improvements to the property that provide lasting benefits.Plumber Labor for remodel: Labor costs for installation or repairs are generally categorized separately from materials.

The LLC is created to protect your personal assets and to separate your personal business from your investment business.  

San Jose is now the first city where an ADU can be sold separately from the main house - I'm not sure how that works, maybe the land is divided up in the assessed value???

Or have ideas on creative lending options as two separate down payments may be too much for us.

Separately, there are plenty of ways to get money out of retirement accounts prior to retirement age (Roth conversion ladder, 72(t) distribution, or just get the match and pay the small penalty).