Don't wait until you have a full catalog. Launch with a single digital file, physical item, or service, and expand once it's actually selling.
Pick a reasonable price based on similar products, and treat it as a starting point — you can adjust once you see real demand.
Your first sales usually come from people who already know you — share it directly before relying on strangers to find you.
The technical side shouldn't be the hard part. Buylib lets you list a product, connect a payment account, and have a working store in the same sitting — so the only thing left to figure out is what you're actually selling.