you don't publish to the server until the site is complete - or as good as complete. The reason for this is that anyone who knows about the domain can see what you have published - once it's on the server on an active domain it's there for the world to see.
I imagine that it's reasonable to assume that nobody knows about your site however, and therefore you would be safe in publishing whenever you like. The big thing to remember is that once you've sent the site to the server there will be two copies of it - one on your hard drive and one on the internet. That means that there's the potential for trouble if you get the two copies out of sync, and forget which one is the latest version. It's possible (and many people work this way) to work on the site live, on the server. If you make changes in this way you can see them instantly in your browser, and all is well............until the next time you publish from your hard drive. FrontPage will then overwrite the server files, undoing all your previous hard work.
Get into the habit of working on the local copy (as it's called) only, and then publishing the changes to the server copy. That way the two will always be in sync.