You have to realize that DC is not a cash flow market, unless you are acquiring apartment buildings.

Or if anyone could shed insight on how acquiring one may impact the other.

I have one property with the plan to acquire many over the next year.

If you're lucky, you may have acquired one in an SFR neighborhood, but unlikely. 

I have not spoken to any CPA but my question is, IF all the the flips are done in an entity - say an S-Corp, and if I use the profit from my flip to purchase the next properties, there really isn't any profit at the end of the year because all the money gets invested into acquiring the next property(ies) until the day I stop flipping, is that correct?

Another thing to consider (if you're looking at the 4% interest paid back to the 401k vs the x% return a 401k investment could generate) is the return you would get from the investment property and whether you could acquire the property without the loan.

And by year 2 or 3, with 1 paid off fourplex & credit in place, acquire next fourplex and start leveraging with loan for acquisition. 

Your home sale is not eligible for the exclusion if ANY of the following are true: You acquired the property through a like-kind exchange (1031 exchange), during the past 5 years.

I just recently enrolled myself into a RE school to acquire my real estate license before starting back up in the fall.

What would be a wise plan of attack as for acquiring a cash flow property in order to invest the returns on future rentals?