i'm asking when do you use the word "sterling" as opposed to "pound." do i say "I have 20 sterling in my wallet." or "I have 20 pounds in my wallet."
No, it's "I have 20 quid in my wallet." Sterling is generally used to refer to the currency when distinguishing it from other currencies, so you might say "pounds sterling" or "British pounds" or just "sterling" if no amount is being discussed. Pounds are used in general conversation to refer to money.
can "quid" be plural? "I have 20 quid in my wallet." or "I have 20 quids in my wallet." How about pence? Am I using pence correctly? "This costs 20 quids and 34 pence." "This costs 20 pounds and 34 pence."