Congratulations!
Welcome to the open waters.
I tried to search just such tales of publications, where we could follow the process and the thoughts behind it step for step. Thank you.
I'm in similar situation with my first English title just launched on Amazon. I'm technically not self-published, but since my publisher is Danish they don't really have a reach here.
A word of advice - I started out as a self-publisher in Denmark 12 years ago before switching to traditional. Starting out with a series is great if the first one is a smash hit - otherwise you are narrowing you target audience.
Empire of Chains has the whole world as potential audience.
The Shadowed Land has only those who read Empire of Chains. Which is not the whole world.
As you build on your succes and strengthen your brand, you might want to consider stand-alone novels. They can cross-pollinate readers, so a fan of one can seek out the others. A series can't really do that, since you can only read them in a specific order.
Like a chain (fittingly) one weak entry will turn of the readership for future novels.
And from a practical standpoint - you are getting better at writing. We all are. Your later installments will hopefully be stronger and better than the earlier titles, but they still depends on readers going through ever one in the series.
I'm putting together an article collecting everything I learned from my launch - review sites, marketing - the works. You might find something useful:
Hunting the Beast
I scooped up Empire of Chains and will take a look.
WormHeart