It's very common to have 2-family homes with a separate entrance for the basement. 

If you know that only the window egress may be the reason for why the ADU is not permitted (not to code), you can take that into consideration in your offer (assuming you have separate kitchen/heating/entrance/...).

My basement is setup as a private studio with its own entrance, tenant will have his/her own laundry and kitchen, not sharing anything with the upstairs.

And as much as I hope my entrance into REI is via a physical property in my/my entity's name, crowdfunding may end up being the way to go (for me) to get started. 

You mentioned landscaping but cutting back trees by the entrance can give a safer feeling to the tenants

A bit more if the meter pan and/or service entrance need to be replaced too.

It only smells in the entrance between the garden and first floor, once you get to the third floor hallway you can't smell it. 

If I may ask, in your opinion, are OKC homes a better overall or starting investment due to their lower entrance cost?

Although it's technically a single family home, it has an attached mother-in-law suite with private entrance so the house functions like a duplex.

Before move-in, I let tenants know our process expectations for maintenance reporting (use the maintenance software) and scheduling-- we enter with 24 hr notice for in-house fixes and tenants are required to schedule directly with 3rd party providers and provide access-- we'll have a service person call to schedule with 48 hours.I also explain how we categorize maintenance issues:emergency (fire or large volume of water) call 9-1-1, urgent these cost someone money, constitute a difficult to avoid safety risk like a loose step to an entrance or missing 1st floor window lock, or cause unreasonable suffering like no hot water or no heat in winter.normal/minor covered maintenance is done at our convenience usually (1-8weeks), upgrade requests may or may not be completed at our discretion and may involve a negotiated cost to tenant.Assuming that you maintain your properties well, getting rid of entitled ******** and managing maintenance expectations is key.