I was planning a chinese coin quilt too. Queen size, I was going to use 6.5 x 18.5" "coins", and I make the quilts generously sized, probably 90-98 x 104". I haven't counted the number of coins needed yet, but I figured 3 columns of coins, and yardage between. It takes more yardage than you think, in my case 3 yards for 4 strips 10" wide. For the coins, I have enough stash to do them.
For a twin sized quilt, you'll need at least 3 yards as well, for the solid yardage between the coins, to get the length of the quilt you want. You'll probably want 2 -3 columns of coins, all showing on the top. You'll have to decide the width and length of each coin. It sounds as if you're going with 2.5" (finishing at 2"). You'll want a width that you can easily cut - you can count on strips being 40" WOF, so cutting them at 10" would be good, and that way you can use layer cakes if you find some that you like. You'll probably want the quilt to be at least 90" long, so you would need 45 "coins" per column. Remember that the width of a twin bed is 39", and you'll want the coins to all show on the top, I'd probably go with 2 columns of coins, that's 20" minus seams, plus yardage 10" wide in between, and you can get 2 columns of 15" or a little more wide out of 3 yards of fabric, so the quilt would be 20" + 10" + 30", or 60" wide minus seam allowances. This would give you about a 10" drop on each side. If you want more, it would require more fabric, either another column of coins or more yardage. For a 90" length of quilt, that would require 2.5 yards of fabric, not 3 yards.