Tankless & storage tanks

Snowmelt

I am going to try to make this short.
I am working on two different laundromats. 1st one has 3 tank-less on the wall and no storage tanks but wants to have 1 or two.
the other has 3 storage tanks and 2 laars units 750,000 Btu's each.
tank-less are the Navien 240 199,000 BTU
the storage tanks are 120 gallon Rheems
1st question is the laundromat is going to have 50 machines total and wants to know now many gallon storage tank do you need to keep up and run out of hot water?
2nd question is the laundromat with storage tank has 85 washing machines and whats to know how many tank-less will you need to keep up. and not run out of hot water?
these two laundromat's came up this same week.

Abracadabra

What kind of washing machines? Capacity?
Top load are around 15gallons
Assuming 2 cycles per hour? 30 gph/cycle?
60gph/machine
50 machines 3000 gph,
50% draw 1500gph
~1/3 of draw in storage = 500gal storage

this is very back of the napkin. i haven't done a laundramat in a long time. there's several other variables to take into account..

aosmith has a decent sizing setup online

kcopp

If I were you I would run this by a Water Htr Mfg.... Brad/ white, State, Etc.
They pay people to figure this out.