I'd definitely say get a comm pricing image done immediately, even if it's just a quick image of "Check out this style, you can get your sona in it for $x!" You can always revise the pricing, options, etc... down the road, but it's gotta be obvious within a few seconds that you're open!
I followed for your art, but I didn't even realize you were open for commissions.

I'd think $20 is a good point just to get you started, but as you get better (and your time gets limited), you can always increase it further.

Ultimately, you know how long it takes to do something. If you're quick at shading, then you can keep the price for shading low. If lineart takes forever for you, then the lineart phase has to cost more. Same with drawing full body timewise vs busts or headshots.

Above everything, don't try to be the cheapest option! There will always be someone cheaper, and you'd sell yourself short.
Bill for your time, because if you're not even doing that, then it's just going to be more stressful for you.

Thank you for your words