Wattpad has literally given me a fear of sequels xD so many people continue first books as seconds instead of having a resolution in the first and a separate plot in the second. Like, you can have your one main plot that spans the series obviously, but each book should have its own plot.
I'm literally afraid that sequels will make me bored of a story or ruin the first book that I've enjoyed.
Please, pretty please, remember the things you were taught in school. Your main plot, climax, resolution, keep them in mind when writing. Your book can go as long as you want it to.
(I don't claim to be a professional, or even good writer. But pLEASE, don't continue one minor plot across two books without a resolution.)