Congrats on your first foray into digital art! I found the transition quite hard but ultimately worth it, you're off to a great start! I'm honestly impressed that this is your first piece. The overall composition is quite good, and those hands! You do quite well on a lot of common stumbling blocks (face symmetry, hands, proportions). I'll give a few suggestions but you should definitely be proud of your work!
There are a couple subtle things with the pose I would change, the left arm is too long (if you try holding something in front of your chest like he is, you'll see that your elbow naturally rests quite close to your side, if you move the elbow joint closer to his side and shorten the arm it will look more natural). Also the right sleeve looks a little off. Fabric is super hard to draw, and you've handled this billowing fabric quite well overall. My tip for this would be to consider where the arm is in the sleeve (even draw a rough sketch in a different layer to visualize). The way clothing hangs depends on what's underneath it. So for example these sorts of sleeves would probably be quite heavy, so you'd expect them to hug the top of the silhouette pretty tightly but hand down loosely below. I'm glad to hear you're already using references, they are your friend and can help tremendously!
I will second what others say about the lineart, you want a brush with pressure sensitivity! It makes your work look way better without you really needing to do much different! I've never used Krita before, but looking at their brush page: https://docs.krita.org/en/reference_manual/krita_4_preset_bundle.html the basic 5- Size default would do the trick. You want something that changes the size of your brush with pressure, but not the opacity for inking. Ideally pressure sensitivity works right off the bat in a program but sometimes you need to check settings for the program and your tablet. Also as sc101 says, pens will have a stability setting, which will automatically help make your lines cleaner. This isn't cheating, getting the tablet to respond to you properly can take some tweaking!
Making accurate clean lines is the hardest part of art (for me at least) so don't be discouraged that it isn't perfect! Making longer lines in a single stroke right off the bat is the right way to do this. It's painful and difficult to do, but you'll get a feeling for it, and it's better to avoid developing bad habits you have to break (I did micro overlapping lines for so long and it just... didn't look good haha). Keep up the good work!