This is a very broad question and without tons of additional info no one credible will be able to provide you a logical response.

Adding an additional panel for the second unit can cost between $5-10k.

Mods, if this is in the wrong area please move or delete.I pay for a monthly service that gives daily updates to the mortgage market, specifically how MBS are trading and market influences that sway pricing.

You can flip when you need to produce cash to buy properties cash or fund additional rentals.

@Philip FeinsteinMost CPAs charge separately for tax prep and advisory services.

Note that conventional loans allow 5% down for multi-families now...It sounds like even with your father's help, you still don't have sufficient funds, much less also having additional reserves...What, may I ask, is your job? 

You also get an additional benefit of depreciating the improvement/house over 27.5 years.

It's free to create an accountAttom Property Data is something my old office used and paid for and was pretty great resource for foreclosures and lispendences.Usually county courthouses will display property data on their websites or you can see it posted there in person ( Free)Property Shark is paid but pretty useful up here in NYC as well.Free is always nice and as someone who's been privileged enough to used the paid services I would add that if you can afford it, pay for a service for a month or so.

I have hired a lot of people over the years to manage my properties and I have never paid them an additional fee to re-rent the property.

Ask your HR department if your company supports an in-service rollover of your 401K to an IRA (which can be a self-directed plan if that's what you want).https://www.401krollover.com/what-is-in-service-401k-rollover-plan/Once I reached a certain age (late 50s), my 401K plan allowed for an in-service rollover.