Assuming that cost is the driving factor, I'd recommend the following breakdown for your 2-table starting stacks:
8 x T25
8 x T100
6 x T500
1 x T1000
1 x T5000
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24 chips = T10000
Using T1000 chips to replace the T25/T100 chips and a combination of T1000/T5000 chips to color-up the T500s, the total set breakdown is:
160 x T25 (35 chips needed)
160 x T100 (35 chips needed)
120 x T500 (45 chips needed)
55 x T1000 (0 chips needed)
29 x T5000 (9 chips needed)
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524 chips (124 new chips needed)
If using all T1000 chips to replace the T25/T100/T500 chips, the total set breakdown is:
160 x T25 (35 chips needed)
160 x T100 (35 chips needed)
120 x T500 (45 chips needed)
100 x T1000 (45 chips needed)
20 x T5000 (0 chips needed)
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560 chips (160 new chips needed)
Without knowing the actual prices for additional T1000 and T5000 chips, I cannot say which option would be less expensive.
Yet another (and probably better) option is to go with 8/8/6/6 starting stacks*, and using T5000 chips for color-ups of the T25/T100/T500 chips:
160 x T25 (35 chips needed)
160 x T100 (35 chips needed)
120 x T500 (45 chips needed)
105 x T1000 (50 chips needed)
20 x T5000 (0 chips needed)
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565 chips (165 new chips needed)
(*note: works for up to 17 stacks, the other three stacks would be 8/8/6/1/1)
However, if the cost of the lower denomination chips is of lesser (or no) concern, I'd go with this:
starting stacks:
12 x T25
12 x T100
5 x T500
6 x T1000
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35 chips = T10000
(note: works for up to 17 stacks, the other three stacks would be 12/12/5/1/1)
Total set (T5000 chips used for all color-ups):
240 x T25 (115 chips needed)
240 x T100 (115 chips needed)
100 x T500 (25 chips needed)
105 x T1000 (50 chips needed)
20 x T5000 (no chips needed)
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705 chips (305 new chips needed)
Lastly, your 8/8/8/5 starting stack proposal requires the following set:
160 x T25 (35 chips needed)
160 x T100 (35 chips needed)
160 x T500 (85 chips needed)
105 x T1000 (45 chips needed)
21 x T5000 (1 chip needed)
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601 chips (201 new chips needed) -- T5000 chips used color-up all of the T25/T100/T500 chips
Hopefully you can plug in your add-on chip costs for each and determine the cheapest upgrade route.