Ask HN: How to launch a side product for a site hosted on Vercel

We have a site in a niche space that is going to be completely ready to launch by end of October. In the meantime we want to launch a side product to gauge interest and to build some basic brand recognition. The way we are planning to do this is by having a subdomain off of our regular domain, hosting this product there and have a "Coming Soon" page as the homepage of our regular site. I have 2 questions regarding this:

1. From a marketing/SEO perspective is this the correct way to go about it? What are some SEO considerations we should keep in mind with something like this? We don't want a situation in the future where our subdomain ends up being more popular than our regular domain. 2. How can we best do this through Vercel? As I understand it, projects on Vercel can only have one production domain. I can create another project and then link the same repository to it but that is causing its own set of problems. Is there a way to add a second production domain on Vercel or some other method that Vercel/Nextjs provides that we can use?