I have (almost) planned out a 5 part book series. The fantasy stuff doesn't really kick off fully until book 2, and i didn't want to bring stuff forward into book 1 to make it more exciting because the whole timeline ive got stored in my ridiculous brain would've turned to mush. but now ive FINALLY got a plot that will (hopefully) make book 1 unique and exciting! my main characters past is a complete mystery (her parents are connected to one of the main villans etc etc) so ive brought in a bit of history so that the reader won't have to wait until book 5 to find out everything. sorry, im getting a bit off track...*ahem* so! anyway... heres the main plot in each book (which all interconnects into the main plot...like harry potter) book 1: revenge + journey (it used to be just journey, but i got so bored when i read it out in my head i felt like jumping off a cliff...) book 2: the chosen one book 3: finding lost ally book 4: WAR book 5: all of the above (sorta...) but sometimes i feel like im missing an OOMPH! in some of them. what made the worlds most popular series today so.........POPULAR???
I mean, it's kind of impossible for us to know how to respond to this with such little description of the books.
In theory that should be good enough, but sadly it isn't. First thing that makes a popular series popular is accurate marketing. Who do you want to sell your book to? If you want to market it to fantasy fans you have to make it more fantasy. If you want to market it to YA you need to have more exciting elements and less world building. If you want to market it to child and spouse abusers, pedophiles and semi-retarded 13-year old girls you make it more like Twilight. Know your audience. If you write a book that has little of all but much of none, you will lack a core audience. If it is romance-fantasy-scifi-horror-comedy, it might be too diverse for readers to love it. Another thing popular series of today share is that they bring something new to the market. You don't have to be the second coming of Descartes, but from what i have observed so far all successful series bring along an innovation. There are dozens of things to which we can attribute a series' success, but it ultimately comes down to one thing: people have to like it.
And, they'll like it if they like the character(s). Marketing can explain some, but not all of the success of popular books. Some of the most popular spread through word of mouth (which admittedly, some astute marketing campaigns exploit to the maximum extent they can), and marketing can give a book a leg up initially. But what it comes down to, is that there has to be something that really connects with the reader, and to a large extent, this is character. A very compelling plot can serve in place of a relatable character, but it really has to be something brilliant and unique. Some of the best-selling books were unexpectedly successful - so it was more than marketing.
Sorry to break it to you, but if you have to DELIBERATELY stall off the real story in order to keep enough for book 2, then perhaps you don't actually have enough story to form a 2-book series in the first place, let alone a 5-book series. If your plan would've turned to mush that should tell you that your plan wasn't working, and there's not enough story to sustain so many books. Having lots of books in a series for the sake of a series (or having lots of books, take your pick) is not a good or real reason for having a series at all. Your "5 book series" look so basic judging from your outline that all of that could be lumped into ONE single book. Really, rather have one single masterpiece, a real polished, unique gem than to spread yourself too thin and end up with 5 books that have been watered down so much they barely have a flavour anymore. If you write padding, your reader will know - heck, YOU will know because while you're writing you might think it's quite exciting, but give yourself enough weeks or months and you'll bore your own self to tears. And then how will you get back all that wasted time? Hone your energy and concentrate rather than being overly ambitious so every page you write is essential - not deliberately push essential stuff back so you can take the reader for a nice and meaningless stroll trying to divert their attention from the much more interesting roaring dragon that they shouldn't see til book 3.
Succesful series work because each volume is a complete story arc in itself. It has a level of conflict/resolution leading to a climax that engages the reader from start to finish. Each book in your series should stand on it's own. The story has to increase in tension and have a resolution at the end that satisfies the reader. Do not set up a reader for "to be continued". It is a huge let-down in my opinion and will make your whole series suffer.