I’m in the same boat. I like to write and to draw, so I’m working towards both of them being in my repertoire. I say if you want to do it, and feel like it’s meant for you, then go for it.
The key to being consistent is developing good habits and having a plan (not just a “finish by this date” plan, but a business and life plan). That doesn’t mean you have to do the same thing every day, though. If you find yourself getting bored, then try having different days on which you do different things. Say, you can switch between writing and drawing on different days. Or, if you pick a few projects, you can rotate between them (though you have to be careful with this, or you run the risk of overloading yourself).
Pick a story you want to do, and use both your writing and art skills for it. Really go all out, and maximize both of your talents. If you want to add a second story, that’s fine, but don’t fall into the habit of starting a million new things if you know you can’t finish them. If you’re someone like me, who works best with multiple, rotating projects, then that’s fine, but make sure that’s actually what suits you first. Make sure you know how many projects you can realistically handle, and make sure you have a schedule/plan for them, so you can stay on track. Make a good plan, and don’t deviate!
Also, spend plenty of time learning about and researching both writing and art. It takes a long time to become proficient at either, and that’s not a bad thing. It’s not realistic to jump in and expect it all to work out without putting in the time first. That doesn’t mean you can’t put work out, but the more you learn your craft(s), the better you’ll be. And the better work you’ll produce.
As far as being a professional, yes, you do need consistency. Any professional writer (or artist) will tell you that you have to learn to do work when you don’t want to, when you’re not inspired, or even when you feel overwhelmed. You have to be able to be consistent. If you’re looking at being a professional, no matter how much you enjoy your job, it’s still a job, and that comes with responsibility. Even if you work for yourself, you have to learn that consistency, or you will end up crashing and burning after a while, or you won’t reach your goals. Learn the hard things now, so that down the road, you can produce work that you’ll be proud of. Find a routine that works for you. I’ve met professionals in both fields who have ADHD, and have learned how they work best, and are doing perfectly well. It’s all about finding that balance.
Basically, I’d say: make a decision. If you want to pursue writing and art, it’s doable, but you have to stick with it. Whatever you want to do is doable, so long as you keep working. Yes, it’s a lot of work, but it’s worth it.
Best of luck to you!