I don't see why you can't publish one post with a 1 and the next time you publish the second post put a 2. No big deal with posts as long as a part of the title is different from your next title. Pages are a little different. I think someone already spoke about the parent child relationship of pages that are related. You can also use categories which I don't use. Hope that helps!
Ed

To help you a little, if its a blog post, then yes put "part 1 of 2" instead of just part 1 this will help the user know that there is more to this post, you then should publish part 2 directly after it, so in the default pagination, it will push the person to the next post which would be part 2 of 2. If however you are creating evergreen lengthy articles, like a tutorial, then I would suggest placing this as pages, with parent child hierarchies, like tutorials/seo-training/the-basics-of-seo-part1/ and then tutorials/seo-training/the-basics-of-seo-part-2/ . This would allow you to continually add extra pages in fact you could have other pages under this parent category that wouldn't need the words "part" at all.

You could put a text link mentioning your 'previous post'. Depending on how people find your posts, they may not read them in order.

yes go to appearance and click on header

maybe this will help The Differences Between Posts & Pages