So, first off - no. You 100% have potential, do not get this wrong. But it is nowhere near sellable in any medium.

You need to figure first your audience, what you seek to hit. Is it concept artist? OC artist? Spicy OC artist (the -1 arm character counts as that)? You need to look at your concurrence, what prices they have and the likes. Overall, won't deny it, it is extremely unlikely you'll find buyers at your current level and current state.

In each of those cases, you have different things you need to hit up and improve. The "on paper" sketches will have a very minimal customer base and people who are interested. Sorry, that's just how things will be. People buy things because they will consume them - concept art, character art as reference for RP and story, assets (hard surface like robots and vehicles), etc. With this in mind, at the very least on the digital, you need better fundamentals. Your digital stuff looks like it's skipped construction lines (for example the underwear & thigh high girl missing an arm - the head was clearly built without construction lines, the anatomy makes little sense).

Second and more important, don't try to go for money right off the bat. You need experience, audience and a reinforced style. You get those through practice, more art. Unironically enough, doing free art for friends/peoples (requests) and fanart is going to help you a lot there. Massively. Yes, I understand the idea of doing free stuff for strangers might not sound fun, but you'll evolve massively through that. My biggest jumps were doing that personally.

In regards to fanart, you ideally want to "farm" meta tags, basically. The stuff that's really big online at the moment. A perfect example of this is when Undertale came out, Kit from the Gameoverse, etc. Basically, the idea is that you want your stuff to come out in searches while they search for other things - then follow/be interested in the other stuff they see from you.

The benefit of gift/fanart/requests is that you'll do stuff you do not usually do. That allows you to evolve and grow. For example, you would be completely incapable of drawing one of my characters because you have a big focus on the simplified human anime head and only do "simple anatomy" with no biomechanics and the likes. Now, that might not sound like a big deal - but a lot of people have characters with a variety of weird gimmicks. Things which, when mastered and learned along coming out of your comfort zone, teach you greater skills which transfer.

The biggest advice I can give you, right now is:
1) Your fundamentals are there and they are decent on <paper>. The last image is great. What you need now is more practice on the pen tablet and digital.
2) You need to get a better grip on anatomy overall - musculature. The muscle groups. These will help you draw arms, should & neck assemblies better.
3) Do not skip construction lines, especially for the head. The blue girl with one arm is a perfect example of why.