How to vacate 15 month-to-month tenants for renovations?

[Tony S.]

Hi all,

I'm under contract to purchase an 18-unit apartment with 15 of the units on month-to-month leases.  

Does anyone have experience vacating multiple apartment units occupied by month-to-month tenants in order to do full rehabs of the units?  I want to be empathetic to the tenants' situations and was thinking of offering "cash for keys" as opposed to simply providing notice to vacate.

  If each unit is currently rented for $600/month, how much do you think I should offer for them to vacate?

How long of a time period do you think I should offer to vacate? Is 90 days enough?  Too long?

Any help, anecdotes, feedback would be greatly appreciated.  Thanks,
Tony