Once we get to the size of the house it's a no go.  

Being that the size of this property pushes me into the “commercial” world, do requirements vary significantly (do commercial loans have the same seasoning requirements, etc)?

At 599 total heated square feet, the small tiny home will feature an open driveway, 3 bedrooms, 2 bathrooms, kitchen, living and dining combo, all electric, with a full size washer and dryer.

You best way to go about this is if you have the target area and properties you like to buy, I would research the local section 8 housing committees and ask them what their rates are and that will give you the actual rental rates they provide.I have a list of my committees and what they allow to pay for example it’s a chart and it will say 1 bedroom $900 , 2 bedroom $1300, etc……

A mistake Investors often make is thinking that the HUD FMR applies to every property of that bedroom size. 

their only advantage is if someone parks bad enough that the remaining spot can only fit a golf car sized vehicle.  

If you can find a 'prefinished slab' company, you should be able to get a regular size kitchen done in granite/quartz for <$2000.IMHO, it is worth it and can justify a rent increase.

Should I use something like propstream to find all acreage that fits my size parameters then just start doing drive-bys to see if it looks like it would work?

This is not a one size fits all game - everyone is different.

Long story short, they recommend a process that basically looks like...Soil scientist --> (septic engineer IF needed) --> site plan --> county approval...We've spoken to a few soil scientists and they all quote 2k-5k to analyze the property for an appropriately sized septic system.