At 20k you most likely wont have many people interested in buying shoutouts because its just too small of an account. I'm not saying you can't achieve your goal though. I just think the majority of your money will come from you reaching out to potential customers as opposed to them contacting you. So that's an extra workload as well. 5 bucks for 20k is a decent deal as long as you have 3-5% engagement. So I could see your plan working out for you but you will most likely have to go out and find those customers.