Since this will be my first deal, I'm looking for any advice and tips on what I should be doing before and after I connect with the seller, to make things go smoothly in case I get a bite! 

Participating in my first city tax auction next week.Any general tips?

@Jonathan BombaciThanks for all the great tips. 

Any tips?

Any tips or advice moving forward?

My dad thought that was a cute trick despite the danger.

Maybe if you're lucky you were able to negotiate with the other tenants to get those units up to market rent as well, further pushing the value upwards (of which there are a few tricks, although the deal would need to make sense without this factor as it is not guaranteed.

Any tips for getting a mortgage with putting 20-25% down? 

There are several of them. https://certifiedtaxcoach.org/five-tips-to-avoiding-the-tax-hazards-of-renting-to-relatives/#:~:text=Rent%20at%20Fair%20Market%20Value&text=If%20they%20rent%20below%20fair,for%20more%20than%2014%20days.

Thanks for the tips!