@Steve Buchanan Sounds like a great value add opportunity. Would be happy to hop on a call and talk more if you would like but Ill put my thoughts here as best I can.
I have done 10% to 30% rental increases on most of my 31 units to date. The lesson I have learned is that I have been too slow to take the plung. I have left a lot of money on the table over the last 3 years and that is no ones fault but my own.
Be prepared for some tough conversations. You will be called a horrible person, told you are putting people on the streets, and you are preventing people from putting food on the table. Do your best to be kind, but its inevitable. Lots of people dont think rationally that you are an investor and the current rents are under market rate. You are the enemy. That said stay strong and hold your ground when you make a decision.
If you can knock out some exterior upgrades prior to the rental increases that will go a long way to goodwill. If tenants can see you are taking care of the place, those with some wiggle room are typically understanding that you raise rents. If the long term goal is to renovate interiors of all units these tenants will help to increase cash flow today but typically hang out for 6months to 18months until they are ready for something new.
How well capitalized are you and how quick do units rent in your area. If 4 move out at once, can you weather the storm until you get them renovated and rented? It sounds like you have a lot of upside on the renovation numbers so if you have the financial backing I wouldnt be afraid of a bunch of people moving out.
Multi family valuation is based on cap rates. $83/month rent increase is $1k a year increase to the NOI. At a 7cap that is $14k in added value to the property. It sounds like you are missing out on $5k a month in rents, aka $60k a year, and at a 7cap that is $857k in property value... I dont know about you, but it sounds like you have a great opportunity to execute a killer project!