Regardless of the industry/website type, use a service like usertesting.com to get some qualitative feedback. It often reveals some of the technical or user experience issues that you can become blind to having worked on the site for so long.

On the day of launch, put some kind of prominent banner or note to users that highlights your technical support or customer service availability.

I assume you had a staging/test environment where you put the site up for some people to test (besides yourself and engineers)? It's important to use a variety of browsers and people to give things a good look over before going live. You have looked at it for too long so you'll gloss over it. Fresh eyes are so very important.

Did you hook up monitoring like NewRelic.com? They have a tool that will ping your site from a variety of locations. They also have insights as to where some bottlenecks might be.

Do you have backups for your database?

Do you have a crash plan? What happens if the site goes down due to load? Are you in a position where you can easily increase the size of your server or add more?

You may want to do some load testing, but it'll likely be difficult now before the launch. It takes a bit of coordination to setup for it...But it's something to think about in the future, especially for capacity planning.

Congratulations on your launch!

As a startup lawyer, I can give you some of the legal checklist items.

First, you should consider forming a corporation or LLC for the startup. If you've already done this then you're off to a good legal start. You should make sure you have a decent set of Bylaws or a good Operating Agreement so that you can document the ownership and management appropriately.

Second, you should ensure that you have a well drafted Terms of Service and Privacy Policy. The Terms of Service should contain information about payment and subscription terms, content restrictions, and appropriate disclaimers. The Privacy Policy should comprehensively list every piece of personal information you may collect and should accurately describe how you'll use or disclose that information.

Finally, you may wish to trademark your app name or logo if it is unique.

Feel free to schedule a call if you have any legal related questions about your startup!