Does a cost seg or bonus depreciation actually help you in any way? 

For example, should we focus on acquiring one high-quality property in a strong market, or would it make more sense to spread the investment across multiple lower-cost units in emerging areas?

However, this has to be the primary residence of everyone on title in order to qualify and even if that were all true, we're still only up to $1M that way.I agree with the other commenters, the parents should continue to own it and live in it as their primary, leave it to the daughter when they pass, and she inherits it at the stepped up cost basis. 

Sub2 is a risky strategy for a long term buy and hold as the longer the deal structure stays in place, the higher the chance that issues will arise (like issues with the loan servicer, insurance, seller filing for bankruptcy, seller dying, seller realizing their DTI ratio and ability to buy their next property is negatively effected and becoming upset about it like in your case, due on sale clause being called, etc.).

Can try to reposition to Class B, but neighborhood may impede these efforts.Vacancy Est: Historically 10%, but 15-20% should be used to also cover tenant nonpayment, eviction costs & damages.Tenant Pool: majority will have FICO scores of 560-620 (approaching 22% probability of default), many blemishes, but should have no evictions in last 2 years.

You'll likely also reduce your cost of living by moving to a stabilized apartment.Depending on the cashflow and debt paydown, you can use this strategy until you've built enough equity to reinvest.On the other hand, getting into a multi-family after refinancing will also help you build substantial equity to rinse and repeat in the coming years.

The cleaning and repairs cost a conservative $2,000 because you did all the work yourself.

At that class of property, the turn overs are costly. 

Would you rather set it and forget it and not need to refi again or rather take advantage of low/no closing costs on this loan and plan to be more aggressive on your rate at the time of your refi?

Pyment is $1,054, but $625 is interest.If you sold current house and bought new one with same mortgage amount, but current interest rate of 7%, the payment would be $1,663, interest amount $1,458.So, the interest cost difference would be $833 month!