There really isn't anything in circulation to look out for. $20 bills seem to have become "ATM coupons" and the supply turns over so quickly that even the previous black and green large-portrait designs are hard to find. It's been years since I've run into one of the older small-portrait bills so they're effectively gone from the average wallet.
That said, there are some nice ones to look for on auction sites and at currency shows. These are generally available at prices that aren't too outrageous:
1950-E FRN; ~$55 circulated, around $100 uncirculated
1934 FRN Hawaii overprint; $75-$125 circ
1934-A FRN Hawaii overprint; $45-$75 circ
1929 National Currency; $25-$125 circ. depending on the issuing district
1928 FRN; $22-$500 circ. depending on the series letter and district
If you have ten, ten dollar bills you will have one hundred dollars. If you have 100 ten dollar bills, you will have 100 ten dollar bills...
10 ten dollar bills
100 hundred dollar bills is more money. 900 ten-dollar bills is a bigger stack of paper.
10
There are no U.S. ten dollar bills with that date. In any case bills dated 1963 and later are mostly only worth face value.
Yes, Singapore uses them.
Ten.
You'd get 10, since 20 ten dollar bills would be 200 dollars. 200 divided by 20 is 10.
Bank
10
10
Most US ATM's only dispense twenty dollar bills. Occasionally you will find one that also dispenses ten dollar bills. Obtaining any amount that is not a multiple of ten is not possible.