There have been areas I have seen that the property does not rent for more, and takes a hit on rents as an Airbnb due to the style of the interior/exterior not matching the area.

My question is: since most lumber comes in 8’ or 10’ (sometimes 9’) lengths and since interior doors, closet doors, trim pieces, etc are also usually designed according to these more standard lengths, is it a really bad idea to have my 2nd story walls at 8’ 6” rather than the standard 8’?

I am not used to interior coordinating, so please let me know if there's a better way. 

I have someone on my team drive by any house we plan to bid on, you can learn a lot just by viewing the exterior of the home and talking to neighbors about the interior condition.

Landscaping renovation, front walkway, lots of interior touches and tweaks.

Landscaping renovation, front walkway, lots of interior touches and tweaks.What was the outcome?

But if it's out of sight, in the INTERIOR of my garage, is this actually enforceable?

It looks like most of the work will be interior. 

To me, 25% done would be: Demo completed, any major exterior/interior issues address (leaks, holes in roofs, foundation work corrections, etc...), and all major materials (window, countertops, doors, etc...) have been ordered. 60% to me would be all electrical rough in, framing, drywall is installed as well as any interior doors.

Long story short, the leases are coming up for renewal in 2 mo - the sister has been great, pays rent in advance and online, she even paid to have the who interior repainted by pro painter and  keeps the place in good shape.