Let's assume you want to make $100k/year. Which is a pretty decent life in most places.
Right now the numbers are showing about $8.30/paying customer. To hit that target will require ~12,000 more subscribers. Not a crazy number.
But, at the conversion rate of .51% (126/24,717 uniques->paying) that means you'll need to get ~298 million uniques to your site (or 56 million signups). That's tough. Getting the entire population of the U.S. to come check out your site requires a huge marketing budget.
If you can convert all signups into paying customers (currently at 2.7% conversion) that goal becomes much closer. About 19% of all uniques are turning into signups (paid or otherwise). That's pretty good. If all of them were paying that's better than 1/3rd of the way there.
So really, for this to work for 1 full-time person to make $100k, conversions free->paid need to go up significantly, but probably pricing needs to go up as well and/or the tiered structure needs to be rethought.