Are you asking if you should wait a year to release the sequel? No, don't wait at all -- the sooner the sequel is available, the sooner you can have readers buy both books! If you have two books available then for every new reader you get, you've doubled the possible sales you'll get, because if they like one book they're very likely to buy the other (and any others in the series that you write in the future). So release them both whenever they're ready and make sure to link the books together so readers can easily jump from one to the other.
There are two e-books that are both free on Amazon.com right now that I recommend you get and read: Successful Self-Publishing by Joanna Penn goes through how to publish the book and some about how to market it; and How to Market a Book by Ricardo Fayet will give you more ideas for marketing. Since you already have the cover art, you can definitely get your book out there without spending another penny, and there are some low-cost ways to get exposure for your book and hopefully get some sales.
Honestly if you need help getting this stuff set up (like turning your manuscript into an ebook or getting it up for sale through KDP), I'd be happy to help you out for free as well. Send me a chat or message and we can figure things out -- or if you think you've got it or maybe just want to start with those books, go for it. Best of luck to you.
When I was looking at self-publishing, this short book helped make it seem less daunting:
https://www.amazon.com/dp/B019H38JL2/ref=cm_sw_r_cp_apa_UbxMFb11T94GG