I am finding better deals that cash flow is stronger in SFHs compared to MFHs, but am worried about scale with SFHs.

Id need to find a way to cut the startup capital down, or verify that it could support more than 50 units for economies of scale.

House hack- learn the business, learn how to be landlord, learn how to find a great deal on a small scale and built equity while you do that.

-After reading several posts regarding the BRRRR cash flow, it seems that a $300/$400 cash flow average per month might be achievable...in order to make the effort worthy, this strategy needs to scale to many more properties (50-100+ rentals)...I am wondering how an investor can manage a bunch of rental properties scattered around a city?

We, however, normally recommend though that you go as big as you can go as that's when economy of scales kicks in, especially with a 3rd Party Management Company. 

Just seeing if any of you know of a private lender that has a loan program that allows investors( who buy and hold real estate) who are looking to scale up their business to purchase a property(without the need to renovate) that's on the market with the intent of refinancing 6months or a year later?

Lenders will love because you are scaling your plan and along the way to will prove that you can manage your project and they will be happy to loan you more money when you finish the first phase.

I hope to be involved in large buy and hold real estate investments/developments because I see great advantage in the economies of scale that can be achieved.

Maybe it's 14 days if xyz is on your credit report, maybe it's 45 days if abc is on your credit report, or maybe it's a sliding scale with 14 days having zero impact, 14-29 having a very reduced impact, and that sort of thing. 

We have looked at some large-scale commercial MF projects in that part of Texas over the past few years.