Best tips for after launch?

Keep the momentum going! Engage with the users that ended up signing up and keep sharing your product across relevant channels. A lot of companies publish a blog article with their Product Hunt experience, you could also do a video or something else to summarize your experience with the platform. Besides that you can stay active in the community, support other products, and connect with fellow makers if you're looking to build partnerships or just learn about new awesome products on a regular basis.

Leverage your connections Have a message prepared from earlier to send to your personal and professional connections across various social platforms and emails.

Requesting reviews on your Product Hub will help with post-launch discovery as well. :) You can do this by going to the review tab on your Product Hub and clicking the 'invite people to review' button.

When you launch, create an exclusive launch offer for all the Product Hunters. Offering discounts to the community members increases the chances of support that you may get.

If your product is outstanding and you’re getting great traction, keep your emails and Twitter’s DM (other social media DMs too) open. You may be contacted by some journalists and bloggers.

I would send a welcome email to people that came from Product Hunt, asking for feedback, letting them know they can always reach you out and tell you what needs to be improved or if they are not having the best experience. In essence, saying something like "hey, thank you for being here, I've still got your back". In a way, they are your early adopters that could help you get new users or support your next launch.