If you plan to scale, I would get one right away on your first property.

@Jerry Zigounakisi'd pick a market close to you, or one you have strong ties in, rather than trying to get to one via math.can you invest where you live, or 1-2 hours from where you live, or where you like to vacation, or where you went to college, or where you plan to move someday?

If you're planning to rehab properties for rental or flipping, a hard money lender might be the right fit.

My father-in-law told me he plans to sell his 6 unit condo building ASAP so he can "retire" from being a landlord.

The cash on cash return is only meaningful when you evaluate it based on your long term plans.

I have employer sponsored plans that match contributions as well as a solo 401k and I do a backdoor Roth. 

It might be worth a follow-up closer to the move-out date to confirm their plans, but avoid excessive contact to prevent escalation.

It depends how long you plan on living.

I've never taken one and don't plan to, but good to hear from someone that went through it.

@Marcos Carbi  If you want to allow a payment plan, Tell them this is the best I can do:Pay $xxx cash by tonight at 8pm for November's rent. and then beginning Monday Jan 20, pay $450 each Monday (in cash?