If your "Retirement account" is a Self Directed IRA, Your LLC (unless owned by your retirement account) cannot do any business with the C-corp or your retirement account.

I flip houses and have a full time corporate office job.

My Entire Life i hustled no matter the stage, the area,the arena, level or competitive sport and i've realized how important the hustle is its a lifestyle its a culture it pertains to everything merchandising,real estate,sports ,corporate america and globally.My Question is How hard are you willing to hustle?

There are advantages to keeping properties under your personal name (types of financing available, ease of financing, down payments, etc.) as well as putting them under an LLC/Corporation (built-in liability protection, etc.). 

So yes things like corporations arose.

And with returns on some approaching 7-8% still with national corporate tenants they can a great fall back (or first line strategy).

Although I have a lot of capital already, and plan to save even more in 2019, I wanted to know - are there tax advantages/disadvantages of opening a corporation/LLC and business account from the very get-go to merely hold this capital until I'm ready to purchase?

Big Corporation will have CFO and highly educated accounting department to manage their debt. 

Originally posted by @Jay Hinrichs:. . . don't think for a minute that rentals are immune.. you have landlords competing for tenants start moving in with family. . . .You might also find people who get downsized from Corporate America will start looking for side hustles to make money.

When I started a business back in 1990 (which failed after a year, but I learned more about business in those 12 months than I ever learned in business school or Corporate America), I attended local networking events related to my field.