For 120 x T20000 starting stacks (8/8/4/7/2) with 100% re-buys (4 x T5000) and color-ups (T1000 for T25/T100, T25000 for T500/T1000/T5000), you'd need the following, rounded up to full racks. Numbers in parenthesis reflect an extra rack per denomination, which is what I'd recommend actually ordering:
T25 x 1000 (1100)
T100 x 1000 (1100)
T500 x 500 (600)
T1000 x 1000 (1100)
T5000 x 800 (900)
T25000 x 100 (200)
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4,400 chips (5,000 total recommended).
6 tables, cash games with stakes ranging from .50-50 to 5/10 NLHE:
50c x 1000
$1 x 2000
$5 x 4000
$25 x 1000
$100 x 1000
$500 x 1000
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10,000 chips, which is just under $1.5 million bank (excluding the $500 chips = another $5 million), or about $246K per table. Works out to $225,000 total in $5 chips and smaller, which is $37,500 per table. Probably wouldn't hurt any to add another 2000 x $1 chips and 3000 x $5 chips, just to be on the safe side.
Limit games are another matter. Every table you spread should have at least 2000 of the smallest denomination. So if spreading 2/4 limit, you'd need 2000 x $1 chips just for that table, plus a couple of racks of $25 chips. If spreading 10/20 limit, you'd need 2000 x $5 per table, plus a rack or two of $100 chips.
I'd plan on at least 20,000 chips total (5,000 tourney and 15,000 cash), and that's assuming no fixed-Limit games are offered. How many extra chips are needed for Limit games will depend on many tables you want to run simultaneously.
Planning for a card room is a lot different than a home game, because it's not a static or fixed-size crowd. Players come and go, move around to other tables, go to dinner and return, etc. Worst thing a casino can do is run out of checks.