I use GIMP 2.0. I have a vertical scrolling comic so I set my width to 940px(max tapas allowance) and my height varies depending on the panel composition (usually shorter). My DPI I set at 300.
I use CSP for drawing & inking the initial page(plus certain FX) at 600dpi. I then color in Photoshop, so that bumps up the res/pixels even more.
i use medibang paint with a wacom intuos pen small! as for resolutions, i used 800x12800, then i use this website19 to cut it into the sizes needed for both webtoons and tapas (huge lifesaver, trust me)
i used to use 800x20000 if you want something bigger to work with.
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I use Medibang Paint and my wacom to make comics!
My resolutions are 700 x 17920 px. Yes, I know the file is big, but it's pretty easy to cut if you don't have photoshop or any of those fancy programs. Once I finish with my comic, I go on this website called Croppy https://knicknic.github.io/croppy/6 who arranges all my files in order, preparing it for whatever platform you want to post your comic on. They have options for both Tapas and Webtoons 
Hope this helped 
Clip Studio Paint for the line art and Photoshop for the coloring part for Cosmos Song3. Each page dimension size varies but it's always 300 DPI resolution.
I use Clip Studio Paint and I work in 2000px wide x any height that the episode demands. Since I'm doing vertical comics the height size can be insane (the first episode of the webtoon that I'm about to launch has more than 40000px of height!). I had to split it on 4 parts so my laptop stops lagging XD
I like to work in a bigger canvas because after I resize the picture to 900px or 800px wide, the art looks smoother.
I use Clip Studio Paint and Photoshop. My image size is B4 size at 600DPI.
Your images have some pixelation so I would recommend working a bit larger and then scale down for the web and save as a PNG-8 or possibly PNG-24. PNG-8 has less colors/information, but your pages look pretty simple and aren't transparent so that might be enough. I save mine all as PNG-8 because the pages are black and white.
I use the followings
1- CLIPSTUDIO Paint - For basically all the drawings and stuff
2- Photoshop - Color correction and to cut the pannels
3- 3DS Max - For modelling the 3D backgrounds
Sometimes I use things like Substance Painter for especific 3D things like textures. I rely a lot on 3D for optimizing my production time, since I have college+work+freelance to suck my time and I'll be damned if I can't update that comic at least twice a month
1 year later
Let's resurface this old post!
I sketch & line my B&W comics traditionally and the rest digitally.
I use VueScan to scan, Photoshop as primary (cleaning scans, fixing linearts, color flating+shading, change flats+shades into tones, lettering) And sometimes Krita (for faster color flating+shading, also when delicate lines need to be re-drawn cos' it's better than Photoshop-- at least using from my not-so-powerful tablet pc)
For Resolutions:
I scan my custom 6.6" x 9.3" comicpages, resize and crop into 5.1" x 7.8" 600dpi, or about 3060x4700 px (that's the printing size without bleed areas)
My output dimensions for Tapas are 750x1155 + extended pixel white gaps = 765x1200 px.
I'm a bit meticulous on formating
Programs I use:
MediBang Paint Pro - For sketching and line art.
Corel Painter Essentials 6 - For flat colors, textures, and shadows. I used it for sketching and line art before I switched to MediBang Paint Pro. Didn't really like using this program for line art.
Adobe Photoshop CS2 - For lettering, outlining speech bubbles, arranging panels, and slicing the comic.
For resolutions, I go for 799px wide and 867px long for each panel or higher than that depending on how much my laptop can handle.
I think your comic looks pretty good in that resolution.
As for my comic, I use MS Paint and Paint.net. MS Paint to plan, rough, outline, ink, and color. Paint.net is to add everything together (the frame, the speech bubbles, etc.)
The resolution is huge: The last comic was 4000x6000 and that was for a 3 panel strip. The height gets bigger the more panels there are. I think it looks nice and sharp, even when shrinking it to fit Tapas.
EDIT:
...and this topic is one year old and you're probably gone! Agh! This is one of the problems I have with these old post being resurrected.
I use clip studio paint and use 800x1280
Though I sometimes start the sketches and thumbnailing in ArtStudio Pro on my ipad mini. I do this due to my day job makes me be away from my computer most of the day.
still using medibang paint, since like 2015? and usually start with a canvas at 940x1080 and make it longer depending on how much canvas i need for a strip. the resolution is always set to 350dpi, keeps it high enough for good quality and not so high that it leaves me with a giant image file
I use 3ds max for the backgrounds, Photoshop for drawing everything that isn't rendered out, and recently i've started using SAI, so far for sketches only since I'm now away from my workstation and my laptop isn't nearly as powerful to handle PSDs for any complex tablet drawing, and SAI still misses a lot of stuff that's invaluable for my work on the comic, like shape or adjustment layers.
I draw at 3535x5000 pixels, and then shrink them down to 900 px wide for publications.