First unit lease is up for renewal on 10/31/2024 and has a good long term tenant.

For now this is based on trust (no contract between me and her) as we are very long time friends and for me is not really about making money at this point as I'm busy regardless, but more of a help to her.

Again, being very focused on key buildings close to new constructions being delivered in 2-4 years, in key growth areas, you can get good deals and cash in apprecitation in the mid-long run.In older buildings, if you are not financially solid, it's recommended to sell before HOA and Special Assessment will put you out of business. 

From a bookkeeping standpoint, this makes everything a lot easier as long as each financial account is used the way it is supposed to be used (no commingling).I would just caution you to think about the functionality of that structure within your day-to-day business operations before pulling the trigger on it.Make sure you're keeping things as simple and efficient as possible.

While it may not be the best CoC that’s considered a solid long term investment cash flow by many.

I was approached by people who are interested in leasing my property long term and use it for cooperate business travel accommodation. 

So 20 year ground contact lumber is okay as long as it’s anchored by cement? 

Many tenants just don't care about the property and many owners look the other way as long as rent is being paid.

I am undecided on if I long, medium-, or short-term rental is the best for me.

In terms of your grandfather living there as long as he's not the owner having a dwelling fire/rental property insurance policy is appropriate.As @Greg Scott pointed out he should have a renters insurance policy whether or not he's actually paying rent.In terms of liability coverage, that depends on what you have to protect so there's no one-size fits all approach.