"To answer your first question, I gave him cash. Nobody else was present to witness the exchange, unfortunately."
Okay, this is your first challenge. While you are in Small Claims court, you say, "I loaned him $1,000.00". What will you say when he responds, "I NEVER, EVER received $1,000.00 from 'Menders' "???? What, if ANYTHING, can you show that you; (1) gave him/her the money, AND (2) that there was an agreement to repay it??? Absent either of those, you have a very weak case.
"How should I send it to him? What is valid proof of delivery (A courier service?)?"
Send it to him using the simplest, least expensive way to be able to prove delivery. Examples are: Certified Mail, Express Mail, FedEX, UPS signature required, private process server, etc. Whatever it takes to be able to show the court that your demand letter was delivered AND received.
"Thank you so much for the advice."
Your welcome.