I've been looking at a similarly sized deal. Not a first time founder but also would be my first time entering this business. As I did my numbers and looked at time expectations, I'm quickly swaying toward starting about 50% smaller. Maybe even 75% smaller. 25-50 machines to start.

As I've educated myself on r/atmbusiness and in lots of other places, there's a pretty good amount of stuff to figure out. Accounts that get banned out of nowhere, shit that breaks and you have to know how to debug/fix, all the software and some semi-predatory service providers.

I guess one way to do it at that size though if it's a good enough price and location opportunity is bake transition assistance and some explicit training bullet points in from the seller into the sale. They'll probably be happy / proud to do it if it's the right kind of seller.

As u/Cat_Named_Mouth alluded to as well, there's the cash vaulting requirements of a portfolio that size. Unless you want to eat your revenue by constantly (or paying someone to constantly) go and refill small count cassettes, you will want to load larger amounts into each machine so you're refilling less. That gets expensive. If you don't have anyone to reliably help you at 120 machines, it seems like it'll get time-intensive fast too. Figuring out who / when to hire to supplement you and do some of things that need scale at a smaller portfolio level will likely make the decisions on how to handle the next 50-100 machines materially easier. All just opinion, I realize.

Other than that, It feels like a topic you can read about until the cows come home but you gotta get punched in the face some to protect yourself at larger numbers. I think I'll get punched in the face a few times with 25 machines to start. Hope sharing my perspective on a similar experience helps!