Whe shopping around you are going to see that some charge more interest but less closing costs and other less interest and more closing costs.

The sub meter costs and monthly reporting fees can be charged to the JADU. 

Repeat clients mean more compensation with lower expenses (leads cost money) AKA more profit.

This raises the cost of using an STR versus using a hotel. 

I ask cause an architect costs money and Im not rich.

Think of it this way - the 6.00% cap rate is your cost of equity.

You've listed what you can get in increased rent, but what would it cost you? 

This includes having a clear understanding of holding costs, financing options, and potential rental income once the property is ready.Your current realtor’s local expertise will be invaluable as you navigate these challenges.

EDUCATE YOURSELF - yes, it will take time, but will lead to a selection that better meets your expectations & avoids potentially costly surprises!

Real Estate is definitely not just a "numbers analysis" and you are definitely thinking about things the right way - but I think a good next step for you would be to spend some time putting a lot of this stuff into a (very) basic financial model/spreadsheets mapping out all the potential costs and estimates on effect (effect on value, on exit, different scenarios) - I think getting started with that framework should help with these decisions immensely