"Style theft" is an entire discussion on its own and I don't have a solid, one-size-fits-all opinion of it. But, if you are knowingly and intentionally doing it, then, for the sake of this conversation, we'll agree that it's a real thing. Copying a style may or may not be an issue for the individual artist you're referencing, but when it comes to re-creating an entire piece of art (style, pose, expression, colors, whatever), it's important to clearly state that it was an inspired work, giving credit to the original artist, and providing a link to their original post. Something like, "This is a practice piece. I used XYZ's "Title of Artwork" as a reference. DM if you have any questions or concerns."
There's nothing wrong with finding your own style through studying and learning from others. However, if you don't personally know the artist and you post your art in an area/category adjacent to theirs, they might feel like you're intentionally ripping them off. So, don't feel bad about learning to draw by duplicating what others do, but, remember to be open about it in your descriptions. If it's not too awkward, try to talk with your inspirations and see how they feel about it. If it's seriously bothering someone, respect that they don't want to be studied, and focus on learning from other resources.
A lot of times, if an artist takes issue with being copied, they might include a blurb in their bio with something like: "Do not copy, trace, or take heavy inspiration from my work". If you see that, respect it. If the artist has a closed account that is only visible to friends, mutuals, or subscribers, resist the temptation of copying what they have chosen to protect. I would also advise to refrain from using anyone's commission examples, YCHs, or Pay-to-Use bases (unless you've paid for them), or anything that is emotionally sensitive, such as pet memorials, break-up art, or romantic gifts that were originally created for that artist's friends.
Instead, be honest and up-front about it. Finding a Free-to-use base could be a good start, because it will lock in the pose, so you can test your skills of duplicating a style without entirely copying a picture, or cloning someone else's characters. There are a ton of DTIYS (Draw This in Your Style) opportunities on social media apps like Instagram and Twitter, as well as Open Collabs that are already partially drawn, where you only need to add your own character. Such ops will negate any accusations that you're committing any sort of theft or shady behavior.
If you do this only for practice and you still have your own art that is unique, maybe you could split your gallery. There are times when I use photographs for practice, to figure out different poses and angles. As much as I like those results, I will not post them. They stay in my own private files, because they were built on things that I did not own. I couldn't ask the models or photographers for permission, and I couldn't credit them. I also wouldn't want people to look at those things and think that that's how I normally draw. I just don't need that kind of stress.
Techniques, though? Yes, I've learned a lot from looking closely at artwork that I admire, and trying to understand what they did to make it look so good. I've learned to use thinner line art, and coloring the lines to be less distracting. From there, I've developed my own style of using invisible lines for small details, which I feel was the point when I starting really liking my art. From there, I moved on to adding even more coloring to my line art layers. It takes literally a bajillion layers to do that, but when I have the time to go all-out, I really do feel like it was worth it.
From studying other artists, I've learned more about realistic shading. (It doesn't show through since my characters are so unrealistic, but, eh, whatevs..) I've learned to (try to) keep a consistent light source and to visualize my characters and scene in a 3D view. If I can't figure out a natural looking pose, I will look for inspiration, and then use my own models (which I've created) to cobble together a mock-up for my own scene. I also focus on the types of details that I'm less experienced with, like makeup, short/neat hair styles, and mouths that aren't scary, fangy, weasel maws. Again, though, this is all "study" and I make it a point to not copy anything directly. I don't save refs to my computer because I don't want to be tempted to trace or steal a color set. That's me, though. Everyone has their own way of learning.
I'm happy to constantly be improving, even if it is a slow process with a lot of trial and error.
I've probably synthesized specific cues from other artists, but I'm struggling to think of what they'd be. My overall style has gone through three distinct phases: my childhood scribbles that were stock and simplistic, the early venture into "pseudo-realism", and my present paradigm, which is basically a refinement of the previous. Funny you mention eyes: the main difference between the last two was getting a better handle on shape and proportion—they went from small circles to larger ovals that produce better expressions.
I've never trained professionally and the long arc amounts to tinkering and reiterating before stumbling on something that works. Doubtless I've incorporated pointers from the works I've seen, but excepting when I'm deliberately mimicking a style for effect, I've never intentionally sought to emulate particular elements.
As to diversity of style: absolutely it's an asset. There's one artist I follow on dA that has blindsided me mutiple times with works that come out of nowhere in a completely different technique to the gallery standard. As somone who took decades just to get one style semi-consistent, I envy such flexibility. :P