MattH it doasnt matter if you have 10,000 songs in your song list , someone is going to ask for something you dont have, so i just look at it this way, i am in charge to entertain the majority so i choose what i perform as long as you are entertaining the majority the minority that usually are not happy no matter what you present to them even if you performed naked up side down would not get their attention perhaps a laugh, so just use songs you know people love and if someone requests a song you dont have , perhaps check it out later and if it appears to be a not most popular song dont waste your time learning it as it probably wont be requested again, the other trick is only use most popular songs that really suit you as a performer and try and choose great songs that most other singers dont do you will then make you stand out to potential clients.
Thats what i have found has kept me bussy as a performer in the last 45 years and i am still performing, mind you my audience is quickly dissapearing but i am adapting to the younger generation , i always use the who, what, where, why rule.
Good luck with ST3