Is this your first project? Assuming it is, I say, “Keep it simple!” Lucky for us, we can start at the top, as it were, by starting our self-publishing journey in Amazon-land, using Amazon CreateSpace and/or Kindle Direct Publishing. (No promotional fees have been paid, or are likely to.) Why lucky? Because Amazon already sells 65% or so of all e-books and can give you access to just about any market or audience segment…everywhere. So, the tools/platforms I recommend, especially for starters, are CreateSpace and Kindle Direct Publishing.
This doesn’t really answer the question, though, does it? As you already have seen, there are dozens, at least, of tools, platforms, distribution channels, and publishing services providers to choose from. I’m just saying if the leading provider of just about everything is free/cheap and easy to use and you get all its massive marketing machine working for you, why not start there? There’s plenty of time to get deeper into the marketplace and engineer the perfect set of capabilities and resources for you. Whatever you decide, best of luck to ya’!