Think it massively depends on the limpiness of your players combined with how annoyed they get when they have to make change all the time. Since I can't or don't want to anticipate that variable I personally would go safe and plan for a rather limpy game. For a 25c/50c my perceived ideal is 16 chips per player (I think a lot of people here would say though it's overkill) but let's stick with with that for those calculations for now.
At 25c/50c you'll need to drop
at least three of those chips for a full orbit whereas at 50c/$1 it's merely but still at least one, so that's a ratio of 3:1. 16 chips divided by 3 would be 5 and a fraction, and since that's an odd number you'd either round up to 6 or down to 4.
I also think it's still good thinking with starting stacks in mind. Just given you plan with exactly one starting stack per seat at a table (i.e. concurrent players).
When anyone rebuys, it's already bonus if they get really small denoms again with their buyin. Giving them higher denoms works just as well at that point because there's still enough fractionals/small denoms in play at that very table so making change is no problem. Someone is bound to have a bigger stack than the others. Unless there is rake
but even then the "house" can make change.
Thinking in racks per table is a bit too... granulary... for my taste.