The plan is if we ever had huge emergencies at our house back to back to back than we would take it out of one of those less liquid accounts.

The University itself has really expanded and upgraded on-campus housing in addition to larger developers coming in and building just a ridiculous amount.

Not sure but larger buildings may have different standards.

When I accumulate enough equity, I would eventually like to be able to liquidate these and replace them with multi-family residential.Is this possible?

They have large asset bases and larger networks, which minimizes their risk if it doesn't pay off.Personally, I am not a speculator.

I have learned about the 50% rule (explained here https://www.biggerpockets.com/blogs/4454/32123-wha...) and was wondering if any seasoned investors saw a problem with using the saved funds in a highly liquid investment vehicle.for example: I save 50% of my rental income in a separate account to compensate for maintenance and vacancies, and use that money to purchase dividend bearing stock.

The benefit is that the funds can be liquidated to cash so that they become FLEXIBLE and can be used for anything (marketing, payroll, operations, office rent, etc)...not just acquisition or rehab like traditional real estate funding sources. 

The more and more the market creeps up, the more larger cash position is required.

@Wendy Gomez:You are learning a super important lesson about leverage and liquidity early in your investing career.You have 3 homes purchased for total all-in cost of $110k and are receiving $650*3*12 = $23,400 per year in rent.  

Fannie/Freddie provides a place to liquidate your loan and get your money back to make more loans and free up the banks capital.