I'm looking into 1) buying-and-holding multifamily properties and 2) constructing tiny houses.

Ask him what value he would add for the upgrades you have.Here is what an appraisal will look at.Garage size might bump you a tiny bit, but honestly probably not much.

Only a very tiny percent every finish the plan out to the end.

Those reports are easily available to landlords these days.It only takes one bad renter to erase 3+ years of profits so the tiny bit you'll spend upfront to properly screen your tenants is well worth it.  

Buy a tiny plot of land in the woods and build a cool little cabin by hand.

TL;DR - Commercial newbie needs to know how to effectively lease up a few shops in a tiny town. 

There is a tiny closest because the stairs going to the basement are on the other side.Do I need to find an architect or interior designer?  

There is a tiny bit of development going on now.

Maybe it's in a slightly less desirable area or maybe it needs a little bit of improvement (so it has a tiny bit more execution risk).

Even a tiny bit of peeling paint will cause a property to fail at appraisal.