You don't owe people an explanation as to why your order is taking time. I suggest taking the tbt when the picture is finished, but before you deliver them, this way you can take your time. Because to be frank, drawing for tbt is drawing for free. It's currency you can get for free, it's virtual, people don't need to be rushing artists when an artist is drawing them something FOR FREE.
Looking at your shop the first post is very long. I think if you can get the point more concisely it might be more inviting, honestly in terms of your rule section, you can boil it down to : "request a drawing and I'll let you know if I can do it! I won't draw anything that breaks forum rules so nothing inappropriate thank you." I think also posing the shop as practice is helpful too, people will know that you're practicing, so won't request anything crazy, but will also have realistic expectations. Your prices are very, very low. I would personally advise changing to a pwyw shop, or freebies with encouraged tipping. You're charging people basically a single post on this website, I honestly think if you change it to pwyw or tipping, people will pay more. I've done freebies in the past (like 2014 lol) and if you encourage tipping sometimes people will tip like 100 bells, way more than what you're asking. Of course, 2014 was a different time on the board too, more activity on the whole.
Other than that, I think you need to make your examples more accessible. I suggest creating an 'art' tag on your art posts on tumblr, and pointing people to that tag for all your work, so they can see your stuff up to current.
Next is about the more practical side of how you capture your pictures. It looks like you're doing it by electric light, and personally I think you could capture them better. The key is making sure you use natural light (so a window) and that you taking the picture are opposite from the light source, this way your art will have no shadow. Also, I'm going to assume your phone has an photo editing feature for cropping and adjusting saturation? A few tips I have with this are, avoid drawing too close to the edge of the page, this way you can always crop your picture to make it stand out on it's own. Also, I see in the post you currently have linked as an example, there's three images of the same picture, I would really advise against doing this, as it's less concise and honestly can confuse the viewer. I know that sounds dumb, how would it confuse them? but its more it's less inviting to the eyes. Also! Really try avoid flash if you can, I'm not sure if it's just your electric lighting, but a flash on pencil lead will make it really shiny and weird looking in a photo.
Now, I know this isn't related to the shop itself, but I will give a few tips on capturing clear photos as well. One thing that is immediately apparent is that you're often drawing using blunt pencils. This makes the image look muggy and dirty, and because the point of contact with the paper is also larger, erasing sketch lines of a blunt pencil is more difficult. I heartily suggest you invest in a few items. A mechanical pencil (0.5 is standard) a lining pen (these can vary but again, 0.5, 0.3, and even 0.1 are commonly used). Learning to use a lining pen, and become confident in your linework, is a very useful skill and will also translate extremely well to digital work, if you choose to do that down the line. These items shouldn't be too expensive and I honestly think you could probably find a lining pen, and a mechanical pencil for under 5 bucks. I use Faber castell. You can get cheap mechanical pencil refills also! you don't have to buy a new pencil every time the lead runs out, just make sure your pencil and replacement match!
I really like your headshots! you show good signs of improvement! Try not to tie your confidence in your art to how much interest others are showing, this is a serious pitfall for any artist. The only thing you can do is keep striding forward.
I don't really know about bumping, but if you turned it into a freebie thread, you could bump it every time you draw a new picture. Even if it's not someones request, bumping with a fresh pic also reminds people what you draw.
Also, good job not shying away from drawing guys! I did that for a long time and it really came back to bite me in the ass lmao. Keep in mind a lot of people will also only request female mayors/ocs, so you have to consistently also self motivate into drawing men.
I'm sorry I went on and on and on hahaha. Best luck and keep drawing. I think I will make a request in your shop... I hope you're ready! If you feel like there's anything else you want help with don't hesitate to pm me if you want, or like this and I can come back and check if you responded, really whatever works.
If you genuinely want to make a lot of tbt, I suggest working on mayors and villagers, because once that switch game hits I can assure you those requests will be coming in hot. But honestly drawing people generally will help, even with the villagers and they're basically just people with really weird heads. Good luck!
Edit! Also I think 7 slots are too many. I think 3-4 slots is better. Even if all 7 slots are empty, 3-4 is more manageable. If you have 7 people waiting, and each picture can take a few days, the the seventh person could be waiting a few weeks. Waiting isn't usually a problem, but I still think simply having less slots is easier to manage.