I was approached with an opportunity and being a newbie I wanted to see is these members made sense to a more seasoned investor.

Question: are there other property managers that take the all-encompassing/OneRate approach, but are much better to work with?

I am not sure about this approach. 

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.

So, as an example, if you look today and you see that various sources lead you to believe that you can rent it for $1500/ month, that number can change quickly in a week (let alone 3 months) based on other factors in your local area - such as a similar property suddenly gets put on the market for rent.In addition, there are different ways to approach your rental amount. 

As I just closed a triplex and want to consider the best approach when sending my Introduction letter.

Have you ever encountered unexpected repair issues during a flip, and what was your approach to resolving them?

The foregoing is not legal advice and is shared for informational purposes only on what I see as a practical approach of how I will address such issues. 

I looked into DSCR and spoke to a few lenders, but it seems I need to have 2 years of rental property ownership before I can utilize; I'm only approaching my 1st year of renting by the room, so I assume I'd need to wait another year before I can look into DSCR.

Getting the lowest balance out of the way is usually the quickest way to start snowballing extra payments into other debts you want to clean up.