Someone once told me that you should stop work on a series after the first book (beyond outlining). First see if you can sell the first book. If you sell it, and it sells well, your publisher will probably want more books. But if it doesn't sell, you wasted your energy writing a book (the sequal) no one wants. Whereas, if you spent that energy writing a new first book in a new series, you'd have another product ready for the market.
I was really tempted to write the second book in my series, and did a few chapters before realizing my time was better invested elsewhere. If anticipate your readers are reading them in a row you may not need to infodump.