Hopefull your father is not that old to encounter this issue(There is a time restriction of 1 year).   

My list of properties is increasing and I am looking to start a direct mail marketing campaign to get in touch the owners of the duplexes.

Possible, with a blanket loan covering both properties, but not advisable....it restricts your ability to sell, refinance, etc. individually.  

Condos are also complicated because you then need to find out if there are rental restrictions in place because they could prevent you from renting at all or other restrictions.

I'm about to embark on a lead gen campaign (direct mail + social media and Google ads). 

I’ll look into off market propertied in Clarksville with direct mail campaigns.

The tax code says very little about the type of assets that can be invested in within a tax-sheltered retirement account.So, from the perspective of the congress and the IRS, mutual funds and real estate are equally OK for tax-favored retirement accounts.For a variety of reasons -some good ones and some not-so-good -  standard IRAs, 401(k)s, & other QRPs impose "artificial" restrictions on the assets that the account can be invested, thereby restricting you to the provided "menu" of investment choices.However, although congress and the IRS don't have much to say about what type of assets your 401k/IRA/QRP - they do care about "self-dealing" with those accounts and have put in place rules to prevent that."

https://wlos.com/news/local/as...Just read this article and thought I'd share.Help me understand this:"An accessory unit, not part of someone’s home, can be rented as a short-term rental as long as the owner follows restrictions around the kitchen definition."

You may not want to restrict yourself to NYC-based accountants.

Currently I have been using Personal Capital Cash, which started at 2.35% APR, and is now at 2.05% and carries no restrictions.