you can add them onto the same vercel deployment (im guessing thats what your talking about) and then if you want you can rewrite them onto better paths (ie dashboard.mydomain.com -> mydomain.com/dashboard)

Not on vercel but anywhere basically

Would i have to host each subdomain stuff seperately?

You can choose to deploy two apps at domain.com and at subdomain.domain.com.

You can also deploy to a wildcard domain *.domain.com, but that would require tightly coupling your domain with your hosting provider (e.g. if you deploy a wildcard domain app on vercel, you need to move the domain to vercel nameservers)

I'm running multiple domains on my app at the moment. TBH the DX to make it happen really sucks (need to use middleware to rewrite) - but it does work