Will all the posts (the comments, the customised template, ...) be the same?or
Will my readers be able to find my blog?or even
Will I lose Page Rank, and if so, how long?These are all valid concerns.
Publishing your blog to a custom domain is pretty much like publishing it to another BlogSpot URL, except you end up with two (maybe 3) URLs, each of which will work equally well.
- The BlogSpot URL.
- The primary URL for the domain.
- A possible secondary URL for the domain.
There's no visible change to the content - it simply republishes to the new (non-BlogSpot) URL. If you want to go back to normal publishing, you republish to BlogSpot. Simple?
Since the BlogSpot URL continues to work, everybody who has the BlogSpot URL bookmarked can continue to access the blog, transparently. You'll experience a brief loss of page rank, but you'll still get some traffic from your established readers, and from the search engines, and other robotic services.
You will have to update your membership in external services, such as search engines and similar robotic processes.
If you are vigorously attentive to the needs of your readers, and external services, your search engine reputation / Page Rank will pick up, somewhat faster than you acquired it originally. And if you publish content and update the blog at the same rate as before you got the custom domain, your search engine reputation / Page Rank will keep on going up, after it has regained its former level. And that's what a custom domain will do for you.