absolutely. a lot of people actually prefer $20s for cash games. i've personally never seen tourneys use 20s, but there is absolutely no reason they couldn't work.
not for a tourney, those are more typically T25 or T5 based. since you are only planning for 6 person games, you can get away with a pretty small set. for example you could do a T20 base tourney, blinds starting at 20/40, with T5000 starting stacks of:
20 x 10
100 x 8
500 x 4
1000 x 2
and you could introduce the rest of the 1000s and the 2000s as necessary for rebuys/color-ups. you have 87,500 in large denoms (500-1000-2000) as broken down now, so this structure could feasibly handle up to 17 total buy-ins of T5000 after color-ups.
so scrapping the 25s and going to 500 chips, a better breakdown for you for might be (i'm assuming you need to buy in increments of 25 based on your OP):
1 x 75
5 x 75
10 x 25
20 x 100
25 x 0
50 x 25
100 x 100
500 x 25
1000 x 25
2000 x 25
that's 475 total, so still 25 to use elsewhere. i'd probably use it on 500s or 1000s, but if you want to play cash games, i assume you would likely need fracs of some sort. so then you could probably drop to 75x 100s and add 50x .25s. that would be enough for 6 players in a $40 buy-in cash game with $0.25/$0.50 blinds to start with:
$0.25 x 8
$1 x 8
$5 x 6
not ideal, but workable.
you also could make one of the chips (2000) non-denominational, get more, and use them as either 2000s or $0.25s, or whatever else you may need. a single non-denom option can really help a lot with flexibility. so something like:
1 x 75
5 x 75
10 x 25
20 x 100
25 x 0
50 x 25
100 x 75
500 x 25
1000 x 25
ND x 75
finally, i have to show you these if you've never seen them, because they are amazing:
https://www.pokerchipforum.com/threads/1830-themed-gaming-chips.41529/