We would need to mortgage our existing portfolio, which we own free and clear. 

Well, there's a lot of questions you should get answered regarding the condition of the buildings and the existing tenants on time rent paying performance.

This occurs when the HOA has inadequate reserves, the HOA fee is too high in relation to the income of the owners, or too high a percentage of owners are not occupying their units.I would definitely insist that the note being held by the seller be assumable, if the above is correct it may be your only way to sell.Additionally you will need to see if the seller owns the property free and clear, or is he wrapping an existing mortgage note within his new seller financed note?

I like existing rentals for a first-time investment.

As such, the plan must be consulted to determine its particular requirements and definitions.Termination of employmentDisabilityTermination of the planSome current employers may allow for partial or full-transfers from 401k and profit sharing plans even if one of the aforementioned triggering events have not been satisfied.One way of determining if your current employer will allow you access your retirement funds while still working for them, is to check the summary plan description (SPD) for the existing plan.

But my favorite strategy is buying houses Subject to the existing mortgage from motivated sellers.

I have a good idea of how I want to get there, I’m just curious of other people’s paths to get there.My original goal with real estate was to provide additional income for retirement; have a couple paid off houses and help supplement retirement income from my 401k, social security (if it still exists), etc.

The apartments are clean, don't need anything and have good existing renters who want to stay. 

I'm a new investor and my knowledge of financing is still growing but the balloon element of the existing loan makes me nervous.

I would advise you simply allow the tenant to go M2M on the existing lease if there has not been any issues.