Okay now I'm thinking...
Stacks:
8 x 25
8 x 100
4 x 500
7 x 1000
Set:
40 x 5
160 x 25
200 x 100
100 x 500
300 x 1000
60 x 5000
20 x 25k
I like this much better than your previous stack or set breakdown. However....
You do not need those extra 40x T100 chips, nor the extra 60x T500 chips. It is inefficient to use either as color-up chips, since both will be subsequently also removed from the table. For that reason -- along with the fact that T1000 and T5000 chips will be future workhorse chips later in the tournament -- either T1000 chips or T5000 chips (or both) should be allocated to color-up the T25, T100, and T500 chips. Also for those reasons, T25 and T100 chips (and arguably T500 chips) should not be used for re-buys, either -- you are merely adding chips into play that must be later removed. A two-table T10000 set will never require any T25000 chips for color-ups (which is not to say that one shouldn't buy any for other reasons).
base set:
40 x T5 (assuming these are for use as bounty chips)
160 x T25 (covers 20 players)
160 x T100 (covers 20 players)
80 x T500 (covers 20 players)
180 x T1000 (covers 20 players, plus 36x for color-ups of T25/T100 chips, plus 4x spares)
10 x T5000 (includes 8x for color-up of T500 chips, plus 2x spares)
-------------------
630 chips
Adding 20x T5000 chips also allows for ten 10K re-buys (about twice as many as needed). If wanting additional chips to make larger starting stacks, then bump up the T5000 counts (by either 20x, 40x, or 60x for T15K to T25K stacks x 20). Adding 10x T25000 (includes 8x for color-up of T1000 chips, plus 2x spares) will cover the larger stack sizes, and adding another barrel of 20 chips (along with those previously-mentioned 60x extra T5000s) allows monster-sized T50000 stacks for 20 players.
Putting all of those together, you get:
enhanced set:
40 x T5 (assuming these are for use as bounty chips)
160 x T25 (covers 20 players)
160 x T100 (covers 20 players)
80 x T500 (covers 20 players)
180 x T1000 (covers 20 players, plus 36x for color-ups of T25/T100 chips, plus 4x spares)
70 x T5000 (includes 8x for color-up of T500 chips, 60x for re-buys and up to T25K stacks, plus 2x spares)
30 x T25000 (includes 8x for color-up of T1000 chips, 20x for up to T50K stacks, plus 2x spares)
-------------------
720 chips
Which is far fewer chips than your proposed 880 chip set above, and yet capable of far, far more.
And if you've fallen into the OCD full-racks trap, then you might consider:
gluttony set:
100 x T5
200 x T25
200 x T100
100 x T500
200 x T1000
100 x T5000
100 x T25000
-------------------
1000 chips